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SMITHSONIAN

CONTRIBUTIONS TO KNOWLEDGE

MOE X XeV- TI

BEVERY MAN IS A VALUABLE MEMBER OF SOCIETY WHO, BY HIS OBSERVATIONS, RESEARCHES, AND EXPERIMENTS, PROCURES

KNOWLEDGE FOR MEN—SMITHSON

(No. 839)

CITY OF WASHINGTON
PUBLISHED BY THE SMITHSONIAN INSTITUTION

Wal

POW NCES Pl sek eae ley

Tris volume forms the twenty-seventh of a series, composed of original
memoirs on different branches of knowledge, published at the expense and
under the direction of the Smithsonian Institution. The publication of this
series forms part of a general plan adopted for carrying into effect the benevo-
lent intentions of James Surruson, Esq., of England. This gentleman left his
property in trust to the United States of America to found at Washington
an institution which should bear his own name and have for its objects the
“increase and diffusion of knowledge among men.’’ This trust was accepted
by the Government of the United States, and acts of Congress were passed
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President, the Chief Justice of the United States, and the heads of Executive
Departments an establishment under the name of the ‘‘ Smrrusontan_ Lystr-
TUTION, FOR THE INCREASE AND DIFFUSION OF KNOWLEDGE AMONG MEN.”’ The
members of this establishment may hold stated and special meetings for the
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of a Board of Regents to whom the financial and other affairs are intrusted.

The Board of Regents consists of two members ex-officio of the establish-
ment, namely, the Vice-President of the United States and the Chief Justice
of the United States, together with twelve other members, three of whom are
appointed from the Senate by its President, three from the House of Repre-
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To earry into effect the purposes of the testator, the plan of organization
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The act of Congress establishing the Institution directs, as a part of the
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art, together with provisions for physical research and popular lectures, while
it leaves to the Regents the power of adopting such other parts of an organiza-
tion as they may deem best suited to promote the objects of the bequest.

Til

IV ADVERTISEMENT

After much deliberation, the Regents resolved to apportion the annual
income specifically among the different objects and operations of the Institution
in such manner as may, in the judgment of the Regents, be necessary and proper
for each, according to its intrinsic importance, and a compliance in good faith
with the law.

The following are the details of the two parts of the general plan of organi-
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DETAILS OF THE FIRST PART OF THE PLAN.

I. To rycrrase Knowxiepce.—It is proposed to stimulate research by offering
rewards for original memoirs on all subjects of vestigation.

I. The memoirs thus obtained to be published in a series of volumes, in a
quarto form, and entitled ‘‘ Smithsonian Contributions to Knowledge.”

2. No memoir on subjects of physical science to be accepted for publication
which does not furnish a positive addition to human knowledge, resting on
original research; and all unverified speculations to be rejected.

3. Each memoir presented to the Institution to be submitted for examina-
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5. The volumes of the memoirs to be exchanged for the transactions of
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work to supply the demand from new institutions.

6. An abstract, or popular account, of the contents of these memoirs to be
given to the public through the annual report of the Regents to Congress.

Il. To rycrease KNow.ence.—lIt is also proposed to appropriate a portion of
the income annually to special objects of research, under the direction of

suitable persons.

1. The objects and the amount appropriated to be recommended by coun-
sellors of the Institution.

2. Appropriations in different years to different objects, so that im course
of time each branch of knowledge may receive a share.

ADVERTISEMENT Vv

3. The results obtained from these appropriations to be published, with the
memoirs before mentioned, in the volumes of the Smithsonian Contributions to
Knowledge.

4, Examples of objects for which appropriations may be made:

(1) System of extended meteorological observations for solving the prob-
lem of American storms.

(2) Explorations in descriptive natural history, and geological, mathe-
matical, and topographical surveys, to collect material for the formation of a
physical atlas of the United States.

(3) Solution of experimental problems, such as a new determination of
the weight of the earth, of the velocity of electricity, and of light; chemical
analyses of soils and plants; collection and publication of scientific facts, accu-
mulated in the offices of Government.

(4) Institution of statistical inquiries with reference to physical, moral,
and political subjects.

(5) Historical researches and accurate surveys of places celebrated in
American history.

(6) Ethnological researches, particularly with reference to the different
races of men in North America; also explorations and accurate surveys of the
mounds and other remains of the ancient people of our country.

I. To pirruse Knowxepce.—It is proposed to publish a series of reports, giving
an account of the new discoveries in science, and of the changes made from
year to year in all branches of knowledge not strictly professional.

1. Some of these reports may be published annually, others at longer in-
tervals, as the income of the Institution or the changes in the branches of
knowledge may indicate.

2. The reports are to be prepared by collaborators eminent in the different
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3. Each collaborator to be furnished with the journals and publications,
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the whole.

5. These reports may be presented to Congress for partial distribution,
the remaining copies to be given to literary and scientific institutions and sold
to individuals for a moderate price.

VI ADVERTISEMENT

The following are some of the subjects which may be embraced in the

reports:

I. PHYSICAL CLASS.

1. Physies, including astronomy, natural philosophy, chemistry and
meteorology.

geology, ete.

z

2. Natural history, including botany, zoology,
3. Agriculture.
4. Application of science to arts.

II. MORAL AND POLITICAL CLASS.

5. Ethnology, including particular history, comparative plilology, antiq-
uities, ete.
6. Statistics and political economy.
7. Mental and moral philosophy.
8. A survey of the political events of the world; penal reform, ete.

Ill. LITERATURE AND THE FINE ARTS.

9. Modern literature.

10. The fine arts, and their application to the useful arts.
11. Bibliography.

12. Obituary notices of distinguished individuals.

Il. To pirruse Knowxiepce.—lt is proposed to publish occasionally separate

treatises on subjects of general interest.

1. These treatises may occasionally consist of valuable memoirs translated
from foreign languages, or of articles prepared under the direction of the
Institution, or procured by offering premiums for the best exposition of a
given subject.

2. The treatises to be submitted to a commission of competent judges

previous to their publication.

ADVERTISEMENT vil

DETAILS OF THE SECOND PART OF THE PLAN OF ORGANIZATION.

This part contemplates the formation of a library, a museum, and a gallery
of art.

1. To carry out the plan before described a library will be required con-
sisting, first, of a complete collection of the transactions and proceedings of all
the learned societies of the world; second, of the more important current period
ical publications and other works necessary in preparing the periodical reports.

2. The Institution should make special collections particularly of objects
to illustrate and verify its own publications; also a collection of instruments
of research in all branches of experimental science.

3. With reference to the collection of books other than those mentioned
above, catalogues of all the different libraries in the United States should be
procured, in order that the valuable books first purchased may be such as are
not to be found elsewhere in the United States.

4. Also catalogues of memoirs and of books in foreign libraries and other
materials should be collected, for rendering the Institution a center of biblio-
graphical knowledge, whence the student may be directed to any work which
he may require.

5. It is believed that the collections in natural history will increase by
donation as rapidly as the income of the Institution can make provision for
their reception, and therefore it will seldom be necessary to purchase any
article of this kind.

6. Attempts should be made to procure for the gallery of art casts of the
most celebrated articles of ancient and modern sculpture.

7. The arts may be encouraged by providing a room, free of expense, for
the exhibition of the objects of the Art Union and other similar societies.

8. A small appropriation should annually be made for models of antiqui-
ties, such as those of the remains of ancient temples, ete.

9, The Secretary and his assistants, during the session of Congress, will be
required to illustrate new discoveries in science and to exhibit new objects of
art. Distinguished individuals should also be invited to give lectures on sub-
jects of general interest.

In accordance with the rules adopted in the programme of organization,
each memoir in this volume has been favorably reported on by a commission
appointed for its examination. It is, however, impossible, in most cases, to
verify the statements of an author, and therefore neither the commission nor
the Institution can be responsible for more than the general character of a
memoir,

OFFICERS

OF THE

SMITHSONIAN INSTITUTION.

WILLIAM H. TAFT,
PRESIDENT OF THE UNITED STATES,

EX OFFICIO PRESIDING OFFICER OF THE INSTITUTION.

JAMES S. SHERMAN,
VICE-PRESIDENT OF THE UNITED STATRS,

CHANCELLOR OF THE INSTITUTION.

CHARLES D. WALCOTT,

SECRETARY OF THE INSTITUTION.

RICHARD RATHBUN,

ASSISTANT SECRETARY IN CHARGE OF NATIONAL MUSEUM.

FREDERICK W. TRUE,
ASSISTANT SECRETARY IN CHARGE OF LIBRARY AND EXCHANGES.

VIII

MEMBERS EX OFFICIO OF THEUINSTIPUTION:

BM ree roman TR TAG sk te te gtraet SU cwksarsarc.a fe acne President of the United States.
SINS We SO FLRMUAINY bar acats sfe-g,css-cors Saree ister chats Vice-President of the United States.
Epwarp Doucuass WHITE ..........-.+++5 Chief Justice of the United States.
CREAR Os AMOK, iso Shy a Megrated aati Secretary of State.

FRAN EIN MAC V RAGE Shc N.. cee oe umbsiendia 6 Secretary of the Treasury.

FEIN OU TIMESON earch ak eende Scheie eae Secretary of War.

Gorge W. WICKERSHAM <..25 0.2.0. 00002 006 Attorney-General.

FANE ele ELT OrGOCKE yeacrraecvek Leslee sarees Postmaster-General.

GHMORGEN VON indir vam 5.2%) ccd Dae wee ess aoe Secretary of the Navy.

WYO dual CON est = 01 ae Ree eras Secretary of the Interior.

OATES AV VATING ONG tak nicicere Sante sceae tateet ca She ean eases Secretary of Agriculture.

COULARE ANAC Ey aucun. cee teehee ize kis iciete 6 Secretary of Commerce and Labor.

Ix

REGENTS.

JamMES S. SHERMAN ..........-. Vice-President of the United States, Chancellor.
Epwarp Dovciass WHITE ....... Chief Justice of the United States.
SHELBY Me CulnoOnenaee a ee Member of the Senate.

Howry Capor Lonce’.:..:...---- Member of the Senate.

AUTGUSTUSGI OM DACONH ts eer eee! Member of the Senate.

JOHN, DAT ZBI sac creer Member of the House of Representatives.
James: 1: MANNS. aye eae Member of the House of Representatives.
Wim M. Howarp .........- Member of the House of Representatives.
James B: ANGRUIN 45 so5.e pees Citizen of Michigan.

AnpREW. 1). WHODEe= 7 Seeeeeee . Citizen of New York.

JoHn B. HenpeErson, JR. ........ Citizen of Washington, D. C.

ALEXANDER GRAHAM BELL ...... Citizen of Washington, D.C.

Gmonge Graws: 4,20.) serene ees Citizen of Delaware.

CHartes F’, CHoarn, JR. ........ Citizen of Massachusetts.

x

CONTENTS.

BAUCUS LOM Gerstner ment hee eRe creXe vay ees hearer barrens eiars Greieis ois anise nlapaiia ili
simois Otncers.~ Members, andunecents.cjacii: semncateetitiiass o4. tcc cs usccaacis vill

ArtictE I (801). LExperimentsin Aerodynamics. ByS. P. Laneury. Published 1891.
4to, 1, 115 pp., 10 plates.

ArTicLE II (884). The Internal Work of the Wind. By S. P. Lanetry. Published
1893. 4to, i, 24 pp., 5 plates. Reprinted 1908, with appendix pp. 25-35
from French edition of 1893.

Articte III (1948). Langley Memoir on Mechanical Flight. Part J, 1887 to 1896, by
SAMUEL PreRPONT LANGLEY, edited by CHartEs M. Manuy. Part IT, 1897
to 1903, by Cuartes M. Manty. Published 1911. 4to, xi, 320 pp., 101
plates.

xI

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE.

— 801 -

HXPERIMENTS
IN

oak Ye A VEC S.

eee byAUN Ea blo Ie

CITY OF WASHINGTON :
PUBLISHED BY THE SMITHSONIAN INSTITUTION.
1891.

COMMISSION TO WHOM THIS MEMOIR HAS BEEN REFERRED.

Professor Srwon Newcomp, U. S. N.
Professor Henry A. Rowianp.
Professor CLEVELAND ABBE.

_ PRINTED BY —
_ JUDD & DETWEILER.

CONTENTS.

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Vit he Component’ Pressure Recordens.020-s4.0 ean ose. wfsisa ties aeeeee 48
VII.—The Dynamometer-Chronograph................-. Ror Arm bre Teoh ec aer 75

Vili DhelCounterpoised! HecentricsPlane ae. oc as ieee demerit s 89

TSK VO CNOLIM Ge CATIA Cina aes Surry Rotten ie agerege tier keree stent NORE eee I eR lere cielo es 94

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Js\7o) af) 0X bb: Ge ar ereticletn c ORO OT A RNEITIOE.C Oa NT aCRN oer Ree REIS ven che ee EI oa 5 109
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JAS AChb- Che Beeb oobiENs oso CUO ED.: Cc aD Onoee 4 Ga tecomer poUcide et ony s Neu abedesmoe 114

(111)

PREFACE.

If there prove to be anything of permanent value in these investigations, I
desire that they may be remembered in connection with the name of the late
William Thaw, whose generosity provided the principal means for them.

I have to thank the board of direction of the Bache fund of the National
Academy of Sciences for their aid, and also the trustees of the Western Uni-
versity of Pennsylvania for their permission to use the means of the observatory
under their charge in contributing to the same end, and I desire to acknowlédge
especially the constant and valued help of Mr. Frank W. Very, who has assisted
me in all these experiments, and my further obligation to Mr. George E. Curtis,

who has most efficiently aided me in the final computations and reductions.

CHAPTER I.
ENERO DIU C MORES:

Schemes for mechanical flight have been so generally associated in the past
with other methods than those of science, that it is commonly supposed the
long record of failures has left such practical demonstration of the futility of all
such hopes for the future that no one of scientific training will be found to give
them countenance. While recognizing that this view is a natural one, I have,
however, during some years, devoted nearly all the time at my command for
research, if not directly to this purpose, yet to one cognate to it, with a result
which I feel ought now to be made public.

To prevent misapprehension, let me state at the outset that I do not undertake
to explain any art of mechanical flight, but to demonstrate experimentally certain
propositions in aerodynamics which prove that such flight under proper direction
is practicable. This being understood, I may state that these researches have
led to the result that mechanical sustentation of heavy bodies in the air, com-
bined with very great speeds, is not only possible, but within the reach of mechan-
ical means we actually possess, and that while these researches are, as I have said,
not meant to demonstrate the art of guiding such heavy bodies in flight, they do
show that we now have the power to sustain and propel them.

Further than this, these new experiments, (and theory also when reviewed
in their light,) show that if in such aerial motion, there be given a plane of fixed
size and weight, inclined at such an angle, and moved forward at such a speed,
that it shall be sustained in horizontal flight, then the more rapid the motion is,
the less will be the power required to support and advance it. This statement
may, I am aware, present an appearance so paradoxical that the reader may ask
himself if he has rightly understood it. To make the meaning quite indubitable,
let me repeat it in another form, and say that these experiments show that a
definite amount of power so expended at any constant rate, will attain more
é. g.. one horse-power thus

economical results at high speeds than at low ones
employed, will transport a larger weight at 20 miles an hour than at 10, a still
larger at 40 miles than at 20, and so on, with an increasing economy of power
with each higher speed, up to some remote limit not yet attained in experiment,
but probably represented by higher speeds than have as yet been reached in
any other mode of transport—a statement which demands and will receive the
amplest confirmation later in these pages.

4 EXPERIMENTS IN AERODYNAMICS.

I have now been engaged since the beginning of the year 1887 in experiments
on an extended scale for determining the possibility of, and the conditions for,
transporting in the air a body whose specific gravity is greater than that of the
air, and I desire to repeat my conviction that the obstacles in its way are not
such as have been thought; that they lie more in such apparently secondary
difficulties as those of guiding the body so that it may move in the direction
desired, and ascend or descend with safety, than in what may appear to be the
primary difficulties due to the nature of the air itself, and that in my opinion
the evidence for this is now sufficiently complete to engage the serious attention
of engineers to the practical solution of these secondary difficulties, and to the
development of an art of mechanical flight which will bring with it a change in
many of the conditions of individual and national existence whose importance can
hardly be estimated.

The way to this has not been pointed out by established treatises on aero-
dynamies, whose fundamental postulates, like those of any other established
science, may be held to contain implicitly all truths deducible from them, but
which are so far from being of practical help here, that from these postulates
previous writers of the highest repute have deduced the directly opposite con-
clusion, that mechanical flight is practically impossible.* Reason unaided by
new experiment, then, has done little or nothing in favor of the view now taken.

It may be asked whether it is not otherwise with statements which are
authorized by such names as that of Newton, and whether a knowledge of truths
mathematically deducible from them, would not at any rate furnish a test to
distinguish the probably true from the probably false; but here it is important
to remember that the mathematical method as applied to physics, must always
be trustworthy or untrustworthy, according to the trustworthiness of the data
which are employed; that the most complete presentation of symbols and pro-
cesses will only serve to enlarge the consequence of error hidden in the original
premises, if such there be, and that here, as will be shown, the error as to fact
begins with the great name of Newton himself.

In this untrodden field of research, which looks to mechanical flight, not by
means of balloons, but by bodies specifically heavier than the air in which they
move, I think it safe to say that we are still, at the time this is written, in a
relatively less advanced condition than the study of steam was before the time
of Newcomen; and if we remember that such statements as have been com-
monly made with reference to this, till lately are, with rare exceptions, the product
of conjecture rather than of study and experiment, we may better see that there
is here as yet, no rule to distinguish the probably important from the probably
unimportant, such as we command in publications devoted to the progress of
already established sciences.

*See paper by Guy-Lussac and Navier, cited later.

INTRODUCTORY. x

There is an excellent custom among scientific investigators, of prefacing the
account of each new research with an abstract of the work of those who have
already presumably advanced knowledge in the science in question; but in this
ease, Where almost nothing is established, I have found hardly any test but that
of experiment to distinguish between those suggestions presumably worth citation
and attention and those which are not. Since, then, it is usually only after
the experiments which are later to be described have been made, that we can
distinguish in retrospective examination what would have been useful to the
investigator if he could have appreciated its true character without this test, I
have deferred the task of giving a résumé of the literature of the subject until it
could be done in the light of acquired knowledge.

T have thus been led to give the time which I could dispose of, so exclusively
to experiment, that it may well be that I have missed the knowledge of some
recent researches of value; and if this be so, I desire that the absence of mention
of them in the present publication, may be taken as the result, not of design, but
of an ignorance, which I shall hope, in such ease, to repair in a later publication ;
while, among the few earlier memoirs that I am conscious of owing much useful
suggestion to, it is just that I should mention a remarkable one by Mr. Wenham,
which appeared in the first number of the London Aeronautical Society’s report,
24 years ago, and some by Penaud in L’ Aeronaute.

The reader, especially if he be himself skilled in observation, may perhaps
be willing to agree that since there is here so little yet established, so great a
variety of tentative experiments must be made, that it is impossible to give each
of them at the outset all the degree of accuracy which is ultimately desirable, and
that he may yet find all trustworthy within the Iimits of their present application.

I do not, then, offer here a treatise on aerodynamics, but an experimental
demonstration that we already possess in the steam-engine as now constructed, or
in other heat engines, more than the requisite power to urge a system of rigid
planes through the air at a great velocity, making them not only self-sustaining,
but capable of carrying other than their own weight. This is not asserting
that they can be steadily and securely guided through the air, or safely brought
to the ground without shock, or even that the plane itself is the best form
of surface for support; all these are practical considerations of quite another
order, belonging to the yet inchoate art of constructing suitable mechanisms
for guiding heavy bodies through the air on the principles indicated, and
which art (to refer to it by some title distinct from any associated with bal-
looning) I will provisionally call aerodromics.* With respect to this inchoate
art, I desire to be understood as not here offering any direct evidence, or

*From dspo0popeu, to traverse the air; 4200p0pos, an air-runner.

6 EXPERIMENTS IN AERODYNAMICS.

expressing any opinion other than may be implied in the very description of
these experiments themselves.

It is just to say, finally, in regard to the extreme length of time (four years)
which these experiments may appear to have taken, that, beyond the fact of their
being in an entirely new field, nearly all imply a great amount of previous trial
and failure, which has not been obtruded on the reader, except to point out
sources of wasted effort which future investigators may thus be spared, and that
they have been made in the intervals of quite other occupations, connected with
administrative duties in another city.

CHAPTER II.
CHARACTER AND METHOD OF EXPERIMENTS.

The experiments which I have devised and here describe, are made with one
specific object, namely, to elucidate the dynamic principles lying at the basis of
the aerial mechanical flight of bodies denser than the air in which they move, and
I have refrained as a rule from all collateral investigations, hewever important,
not contributing to this end. These experiments, then, are in no way concerned
with ordinary aeronautics, or the use of balloons, or objects lighter than the air,
but solely with the mechanical sustentation of bodies denser than the air, and the
reader will please note that only the latter are referred to throughout this
memoir when such expressions as “ planes,” ‘‘ models,’ “mechanical flight,”
and the like, are used.

The experiments in question, for obtaining first approximations to the power
and velocities needed to sustain in the air such heavy inclined planes or other
models in rapid movement, have been principally made with a very large
whirling table, located on the grounds of the Allegheny Observatory, Allegheny,
Pa. (lat. 40° 27’ 41.6’; long. 5" 20" 2.93°; height above the sea-level, 1,145 feet).

The site is a hill on the north of the valley of the Ohio and rising about 400
feet above it. At the time of these observations the hill-top was bare of trees
and of buildings, except those of the observatory itself. This hill-top is a plane
of about three acres, of which the observatory occupies the south side. The
ground slopes rapidly both toward the east and west, the latter being the quarter
from which come the prevailing winds.

The general disposition of the grounds of the observatory buildings, of the
engine, and of the whirling table is shown in plate I. The whirling table is
shown in plate II, in elevation and in plan, and with details on an enlarged scale.
It has been constructed especially in view of the need of getting the greatest
continuous speed thus attainable, under circumstances which should render
corrections for the effects of circular motion negligible, in relation to the degree
of accuracy aimed at.

The first disturbing effect of circular motion to present itself to the mind of
the reader will probably be centrifugal force; but in regard to this he may observe
that in all the pieces of apparatus hereafter to be described, the various parts are
so disposed that the centrifugal foree proper, viz., the outward thrust of the plane

(7)

8 EXPERIMENTS IN AERODYNAMICS.

or model which is the subject of experiment, shall not disturb or vitiate the
quantitative data which are sought to be obtained.

On the other hand, the effects of circular motion, as regards the behavior of
the air in its enforced circulation, are only to be obtained, as I believe, empir-
ically, and by very elaborate experiments; the formule that are likely to
present themselves to the reader’s mind for this computation, largely involving
the very errors of fact which the experiments here described are meant to
correct. This class of corrections is, then, only approximately calculable, and
we have to diminish their importance by the use of so large a circle that the
motion can be treated as (for our purpose) linear. ‘To show that these corrections
are negligible in relation to such degree of accuracy as we seek, we may advan-
tageously consider such a numerical example as will present the maximum error
of this sort that obtains under the most unfavorable circumstances.

Let this example be the use of a plane of the greatest length hereafter
described in these experiments, viz., 30 inches, and let us suppose its center to be
at the end of a revolving arm 30 feet in length, which was that employed.

Let us suppose the plane to be so disposed as to cause the effect of the
inequality of air resistance arising from the circular motion to be a maximum,
which will presumably be the case if it is placed parallel to the arm of the whirling
table, so that there is also presumably the greatest possible difference between the
pressure on the outer and the inner half. Under these circumstances it is assumed
in the experiments detailed in the following chapters, that the whole plane may
be treated as moving with the linear velocity of its center, and it will be now
shown that this assumption is permissible. The portions of the plane as we pro-
ceed outward from the center, are exposed, on the whole, to a greater pressure,
and as we proceed inward to the center to a less. Using, in the absence of
any wholly satisfactory assumption, the well-known one implicitly given by New-
ton in the Principia, that the pressure of the air at every point of the plane is
strictly proportional to the square of the velocity with which it is moving (thereby
neglecting the secondary effect of the mutual action of the stream lines on each
other), the pressure at the inner end of the plane is proportional to (28%)’= 826.6 ;
at the outer end to (314)*=976.6, and at the center to (380)°=900. The mean of
these pressures at the inner and outer ends, viz., 901.6, differs from the pressure
at the center by 1.6, or less than one-fifth of one per cent., and @ fortiori the inte-
grated pressure over the whole area in this and still smaller planes, differs from
the pressure computed with the velocity at the center, by less than the same amount.
The example will, it is hoped, make it sufficiently clear that such disturbing
effects of air-pressure arising from circular motion, are for our purposes negligible,
and the precautions taken against other detrimental effects, will be evident from a
consideration of the disposition of the apparatus employed in each case.

CHARACTER AND METHOD OF EXPERIMENTS. 9

Most of the various experiments which I have executed involve measure-
ments of the pressure of air on moving planes,* and the quantitative pressures
obtaining in all of these experiments are of such magnitude that the friction of
the air is inappreciable in comparison. This fact may be stated as the result,
both of my own experiments (which are here only indirectly presented) and of
well-known experiments of others.+ —_[t will be seen that my experiments implicitly
show that the effect of friction on the surfaces and at the speeds considered is negli-
gible, and that in them I have treated the actual air-pressure as being for practical
purposes normal to the surface, as in the case of an ideal fluid.

The whirling table consists essentially of two symmetrical wooden arms, each
30 feet (9.15 meters) long, revolving in a plane eight feet above the ground. Each
arm is formed of two continuous parallel strips united by struts as shown in the
plate, and is made at once broad and thin, so as to possess the requisite lateral
strength, while opposing as little resistance to the air as possible, its vertical
rigidity being increased by guys. The arms are accordingly supported by iron
wires extending from a point in the axis about 8 feet (2.5 meters) above the table.
An enlarged section of the lower end of the axis is given in the plate, showing the
lower bearing and the position of the bevel-wheels connected with the shaft, which
is driven by the engine. A lever is also shown, by means of which the table may
be lifted out of its gearing and revolved by hand. The gearing is so disposed
that the direction of rotation is always positive—i. e., clockwise to one looking
down on it. The whirling table was driven first by a gas-engine of about 1} horse-
power, but it was found inadequate to do the work required, and, after October
20, 1888, a steam-engine giving 10 horse-power was used in its stead. This
was a portable engine of 10-inch stroke, having a fly-wheel giving from 60 to
150 revolutions per minute, but ordinarily run at about 120 revolutions, with 90
pounds of steam. The belt of either engine communicates its motion to a set of
step-pulleys, by means of which four different velocity-ratios can be obtained.
These pulleys turn a horizontal shaft running underground to the axis of the
turn-table, as indicated on the ground plan of the engine-house at A, and also

* Since it is impossible to construct absolutely plane surfaces at once very thin and yery rigid, those “ planes”
in actual use have been modified as hereafter described. They have all, however, it will be observed, square and
not rounded edges, and it should be likewise observed that the values thus obtained, while more exactly
calculable, give less favorable results than if the edges were rounded, or than if the section of the plane were
such as to give “stream lines.”

+ There is now, I believe, substantial agreement in the view that ordinarily there is no slipping of a fluid
past the surface of a solid, but that a film of air adheres to the surface, and that the friction experienced is
largely the internal friction of the fluid—. e., the viscosity. Perhaps the best formula embodying the latter is
given by Clerk Maxwell in his investigation on the coCflicient of the viscosity of the air. This is » = 0.0001878
(1 +.0027 0), » and @ being taken as defined in his paper on the dynamical theory of gases in Phil. Trans., Vol.
civ. By this formula the actual tangential force on a one-foot-square plane moving parallel to itself through
the air at the rate of 100 feet a second is 1,095 dynes (0.08 poundals), or less than ;'; of 1 per cent. of the pressure
on the same plane moving normally at this speed, and hence theory as well as observation shows its negligibility.

2

10 EXPERIMENTS IN AERODYNAMICS.

on the elevation at A’, where it is shown as geared to this vertical axis by a pair
of bevel-wheels, that of the shaft having 15 teeth and that of the turn-table axis
having 75 teeth, or 1 to 5. The cone-pulleys used from the beginning of the
experiments up to September, 1890, have four steps with diameters of 21%, 183,
118, and 8 inches. The speeds given by these pulleys in terms of whirling-table
revolutions for 1,000 revolutions of the gas-engine are approximately—

Wowwestispeed aanraaiwl oats ectslonesie eisetss ta crete 25
Seconda ee i eee oe Ee eee eer ie 5O
Third REG rR etc 5 ones LOS ES h md ae cin ctr 100
labdies|p ee Sacogucacuneonusoooesesps tae deo bec 200

The gas-engine speed varied from 180 to 190 revolutions per minute.

In September, 1890, the above-described pulleys were replaced by a larger
set of three steps, having diameters of 36, 254 and 18 inches, respectively, which
give speeds in the ratio of 4, 2, and 1, and the gear, which had broken, was
replaced by a new one of 1 to 4.

This system gives for 120 revolutions of the steam-engine per minute,
driving—

18 in. pulley, 48 revolutions of turn-table per minute = 100 + miles per hour at end of arm.
Oy OO « « re 0) ae « re «
98 «KO « « « mais, cle: « «

By regulating the speed of the engine any intermediate velocities can be
obtained, and thus the equipment should be susceptible of furnishing speeds
from 10 to 100 miles per hour (4.5 to 45 meters per second); but owing to the
shipping of belts the number of turn-table revolutions was less than this for
the higher velocities, so that the highest attained in the experiments did not
reach this upper limit, but was a little over 100 feet (80 meters) per second, or
about seventy miles per hour. The precise velocity actually attained by the
turn-table is determined, quite independently of the speed of the engine, by an
electrical registration on the standard chronograph in the observatory. The
electrical current passes into four fixed contact-pieces (shown at O-P, plate II,
and on large scale in plate III) fastened to a fixed block placed around the
axis of the whirling table, these fixed pieces being placed symmetrically around
the axis, while another platinum contact-piece is fastened to a horizontal arm
screwed into the axis of the turn-table and revolving with it, thus ‘ making
circuit ’’ every quarter revolution of the table. The current passes out of the axis
through a brush contact, shown in plate III, and thence to the chronograph in the
observatory. © designates the fixed contact pieces, and P the platinum piece
revolving with the axis. Sand L are adjusting screws. ‘Turning again to plate
II, an additional brush contact, shown at B, and again at B’, serves to transmit

CHARACTER AND METHOD OF EXPERIMENTS. 1]

a current to wires running out to the end of the whirling arm, so that seconds
from the mean time clock and other phenomena ean be registered on the recording
cylinder of the dynamometer chronograph at the end of the arm; and also
phenomena taking place at the end of the arm ean be registered on the chrono-
graph in the observatory. By these means the experiments are put under
electric control and perfect knowledge is obtained of the velocity of the turn-
table at the moment when any phenomenon occurs. This brush contact was
made sufficiently large and heavy to transmit a current from a dynamo to an
electric motor placed on the whirling arm, and, having this electric equipment
extending to the outer end of the whirling arm, different pieces of apparatus
were devised for registering pressure and other phenomena there.

The whirling table was thus established and the experiments conducted in
the open air, not through choice, but because the erection of a large building
specially designed for them was too expensive to be practicable. It was hoped
to take advantage of calm days for the performance of experiments, as in a calm,
a whirling table in the open air is under the best possible conditions, for in a
confined building the rotating arm itself sets all the air of the room into slow
movement, besides creating eddies which do not promptly dissipate. Practically,
however, these calm days almost never came, and the presence of wind currents
continued from the beginning to the end of the experiments, to be a source of
delay beyond all anticipation, as well as of frequent failure.

In the latter part of April, 1889, an octagon fence 20 feet high (shown on
plate I) was erected around the whirling table with the object of cutting off, to
some extent, the access of the wind. This, however, proved to be ineffectual, and
the difficulty experienced from the wind continued nearly unabated.

If any one should propose to repeat or extend these experiments, I would
advise him, first of all, and at all costs, to establish his whirling table in a large,
completely inclosed building.

CHAPTER ITI.
THE SUSPENDED PLANE.

The first instrument, called the Suspended Plane, was devised to illustrate
an unfamiliar application of a known principle. I call the application ‘“ un-
familiar’? because distinguished physicists have held, for instance, that a bird
(which obviously expends a certain amount of muscular effort in simply hovering
in the air) must expend in flight all the effort required for hovering, together
with so much additional energy as is required to overcome the resistance of
the air to its horizontal motion, so that the energy expended increases with the
velocity attained,* while the consideration of the action of the suspended plane
indicates, if it do not demonstrate, that the opposite view is the true one, and
thus serves as a useful introduction to the demonstrative experiments I have
spoken of as coming later.

* This view of flight received indorsement from a source of the highest authority in a report by Gay-Lussac,
Flourens, and Navier, accepted and published by the Institute of France in 1830. [Navier, C. L. M. H.—Rapport
sur un Mémoire de M. Chabrier concernant les moyens de voyager dans J’air et de s’y diriger, contenent une
nouvelle théorie des mouvements progressifs. (Commissaires, MM. Gay-Lussac, Flourens, et Navier, rapporteur.)
Paris, Mém, Acad. Sci. x1, 1832 (Hist.), pp. 61-118.] The report is drawn up by Navier, to whom the mathe-
matical investigation is due. He formulates the differential equations of motion for the two cases of hovering
and horizontal flight, integrates them in the customary way, assumes approximate values for the constants of
the equations, and computes the work expended by an ordinary swallow with the following results: For
hovering, the work done per second by the swallow is approximately equal to the work required to raise its own
weight eight meters. While in horizontal flight the work done varies as the cube of the velocity, and for 15
meters per second is equal to 5.95 kilogrammeters per second, or enough to raise its weight 390 meters. This
is fifty times as much as that expended in hovering, or in English measures, over 2,500 foot-pounds per minute,
which is a rate of working greater than a man has when lifting earth with a spade.

The same computation applies to any larger bird whose weight bears the same ratio to the extent of its
wings. In view of these figures Navier suggests that there exists the same ratio between the efforts necesssary for simple
suspension and for rapid flight as exists for terrestrial animals between the effort required for standing upright and that
required for running. [Nous remarquerons la grande différence qui existe entre la force nécessaire pour que l’oiseau
se soutienne simplement dans V’air, et celle qu’exige un mouvement rapide. Lorsque la vitesse de ce mouvement
est de 15" par seconde, on trouve que cette derniére force est environ cinquante fois plus grande que la premiere.
Ainsi l’effort qu’exerce l’oiseau pour se soutenir dans l’air est fort petit comparativement 4 l’effort qu’il exerce
dans le vol. Il en coute peut-étre moins de fatigue 4 V’oiseau pour se soutenir simplement dans lair, eu égard 4
la fatigue qu’il est capable de supporter, qu’il ne’en cotite 4 Vhomme et aux quadrupédes pour se soutenir debout
sur leurs jambes.”—Paris, Mém. Acad. Sci. x1, 1832 (Hist.), p.71.] The supposed elegance and validity of
Navier’s mathematical processes, and especially the elaboration with which they were carried out, appears to
haye obscured the absolutely inadmissible character of these results, and they received the unqualified adherence
of the remainder of the committee. This report thereupon became a standard authority upon the theory of

flight, and continued to be so accepted for many years.
(12)

THE SUSPENDED PLANE. 13

The suspended plane (plate TV) consists of a thin brass plane one foot square,
weighing two pounds, hung vertically by a spring from a surrounding frame.
Eight delicate friction rollers AA’, BB’ enable the plane to move freely along
the frame, but prevent any twisting or lateral motion, the use of the guide-frame
being to prevent the plane from so “ flouncing ” under irregular air currents that
its pull cannot be measured. The guide-frame carrying the plane turns symmet-
rically about an axis, CC’, so that the gravity-moment about the axis is simply
the weight of the plane on a lever arm measured from its center. The axis
CC’ rests upon a standard which is placed upon the whirling arm. A pencil, P,
attached to the plane is pressed by a spring against a registering card at the side
of the plane and perpendicular to it. The card contains a graduated are whose
center is at C and whose zero angle is under the pencil point at the vertical
position of the plane. The distance of the trace from the center C registers
the extension of the spring.

When the plane is at rest the extension of the spring measures the weight
of the plane. When the plane is driven forward horizontally the pressure of
the wind on the plane inclines it to an angle with the vertical, and the higher
the speed the more it is inclined. Vor any position of equilibrium there is
neither upward nor downward pressure on the guide-frame, and the whole
resulting force acting on the plane, both that of gravity and that arising from the
wind of advance, is borne by the spring.

The apparatus being mounted at the end of the arm of the large whirling
table and being still, the weight of the plane is registered by an extension of
the suspending spring corresponding to two pounds. Next, lateral motion being
given (from the whirling table) and the plane being not only suspended but
dragged forward, the spring is seen not to be extended further, but to contract,
and to contract the more as the speed increases. The drawing contains a copy
of the trace made by the pencil upon the recording sheet, showing how the
spring contracts with the increasing angles of the plane with the vertical, where
these angles correspond to increasing velocities of translation, or, we may almost
say, to increasing speeds of flight. The experiment also calls attention to the
fundamental circumstance that in the horizontal flight of an aeroplane increasing
speeds are necessarily accompanied by diminishing angles of the plane with the
horizontal.

The experiment may perhaps be held to be superfluous, since the principle
involved, that the pressure of a fluid is always normal to a surface moving in it,
is already well known; but we must distinguish between the principle and its
application. Though when attention is called to it, the latter is seen to be so
immediate a consequence of the principle as to appear almost self-evident, I must
still call the application “ unfamiliar” since, as will be seen, it indicates the way

14 EXPERIMENTS IN AERODYNAMICS.

to consequences Which may appear almost paradoxical, such as that in horizontal
frictionless flight, the greater the speed, the Jess the power required to maintain it.
I do not mean that this illustration as here given, offers a satisfactory demonstration
of this last consequence, but that any one who has really always possessed the
idea that the experiment suggests, in its full import, must have been inclined to
admit the possibility that machine flight grows more and more economical of
power as higher speeds are attained—and this is not self-evident.

‘This preliminary apparatus can indeed, with little modification, be used to
demonstrate this fact, but it is actually presented here, it will be noticed, not as
demonstrative, but as illustrative, of the possibility suggested ; a possibility whose
fundamental importance justifies, and indeed demands, the fullest demonstration,
which can be better supplied by apparatus designed to give data of precision for
computing the actual work done in flight at different speeds; data which will be
furnished here subsequently from quite other experiments.

CHAPTER IV.
THE RESULTANT PRESSURE RECORDER.

As preliminary to obtaining the data mentioned at the close of the last
chapter, it is desirable to determine experimentally the direction of pressure of
the air, (since the air is not an ideal fluid such as the theory contemplates,) on an
inclined plane, and to investigate the assumption made by Newton that the
pressure on the plane varies as the square of the sine of its inclination.

The second instrument constructed was, then, for the purpose of obtaining
graphically, the direction of the total resultant pressure on an inclined plane
(in practice a square plane) and roughly measuring its amount.* For this reason
it will be called here the Resultant Pressure Recorder.

DESCRIPTION.

Plate V contains drawings of the instrument. Upon a base-board, BBY, is a
standard, E, carrying an arm, AA’, hung symmetrically in gimbal joints. On
the outer end of the arm a one-foot-square plane (called here the wind plane) is
fastened with a clamp, and a graduated circle assists in setting the plane at
different angles of inclination to the horizon. The extremity of the inner end of
the arm earries a pencil, P, which registers on the surface of a vertical plane, which
is in practice a sheet of diagram paper clamped on the surtace FF’ of an upright
circular board fixed by a standard to the base-board BB’. The pencil-holder H
fits closely into a ring at the center of a system of four equal radial springs attached
to a circular frame, MM’, projecting immediately in front of the registering
board and concentric with it. This frame MM’ is connected by supports to a
close-fitting ring, which closes around the registering board and serves as a holder
for the diagram sheets which are, as stated, clamped on the face FI” of the cir-
‘ular board. The radial-spring system and its frame may be rotated about the’
registering board, so that the diagram sheet may be rotated in its own plane.
The inner or recording end of the arm is weighted so as exactly to counterpoise
the outer end carrying the wind plane. Hence this plane is virtually weightless,

* Observations of the pressure on inclined planes haye been made by previous e xperimenters, the first being
by Hutton in the summer of 1788, just 100 years before those about to be recorded. But in the experiments of
Hutton, as well as in most of the later ones, the horizontal component of the pressure on the inclined plane has
been the subject of measurement, while the apparatus about to be described affords a measurement of the total

normal pressure on the plane.
(15)

16 EXPERIMENTS IN AERODYNAMICS.

and when the apparatus is at rest the pencil-point rests in the center of the
radial springs without pressure upon them, but when any force changes this
position of equilibrium it is resisted and measured by the resultant extension of
the four radial springs, shown by a definite departure of the pencil from the
center in a definite direction.

The tension of these springs is determined before the apparatus is mounted
for trial, by rotating the frame MM’ about a longitudinal (imaginary) axis passing
through the centers of the wind plane and registry plane. If the pencil end of
the arm be weighted with (for instance) one pound, it traces out a curve on the
paper corresponding to aone-pound tension in every direction. With two pounds
another and larger curve is described, and so on till the resultant pressure of the
four radial springs are then tabulated for every direction and every pressure
which the wind of advance may later be expected to exercise. These curves are
in practice very nearly circles.

The distance from the pencil to the gimbals is the same as that from the
gimbals to the center of the wind plane, so that the wind pressure, considered as
acting at the center of the plane, has the same lever arm as the pressure
imposed by the extended springs. It should be particularly noted as a con-
sequence of the above-described conditions that, although the wind plane is
perfectly free to move in every direction, it is not free to rotate—i. ¢., it is
always during this motion parallel to itself.

The only other feature of the construction to be noted is the combination of a
spring and an electro-magnet connected with the recording pencil. The pencil is
held away from the paper by means of the spring until a desired velocity
of rotation of the turn-table is attained, when by means of the electro-magnet the
pencil is released and allowed to record.

The method of using the apparatus is as follows: The wind plane is set at
an angle of elevation @; a disk of paper is placed upon the recording board and
oriented so that a line drawn through its center to serve as a reference line is
exactly vertical. The whirling table is then set in motion, and when a uniform
velocity has been attained a current is passed through the electro-magnet and
the pencil records its position on the registering sheet. Since gravity is virtually
inoperative on the counterpoised plane, the position of this trace is affected by
wind pressure alone and is experimentally shown to be diametrically opposite to
its direction, while the radial distance of the trace from the center is evidently a
measure of the pressure on the plane. Thus the instrument shows at the same
time the direction and magnitude of the resultant wind pressure on the plane for
each inclination of the plane and for different velocities of the whirling table.
Since the arms of the apparatus are exposed to the wind of rotation, the outer
end, moving with greater velocity than the inner end, will be subject to a slightly

THE RESULTANT PRESSURE RECORDER. 17

greater pressure. Preliminary experiments were therefore made without the wind
plane for detecting this effect, with the result that no sensible difference was
apparent between the pressure on the inner and outer arm, even at the highest
speeds.

On August 25, 1888, the spiral springs were calibrated by hanging weights
of 1, 2, and 3 pounds to the center of the springs and marking the displaced
position of the center when the system was rotated through successive octants in
the manner already described. Experimental circles were drawn through the
system of points, and, the departures of the individval points being very small,
the circles were adopted as the curves giving the relation between pencil excursions
and pressures. From these curves the following table has been constructed :

TABLE I.
Excursion of trace. | Pressure. || Excursion of trace. | Pressure.

Centimeters. Lbs. \Grammes.| Centimeters. Lbs. |Grammes.|
0.28 O.1 45 | 4.45 ey ap ete}
0.55 0.2 91 | 4.73 Li iia
0.82 0.3 136 || 5.03 1.8 816
1.10 0.4 Sie 5.39 1 862
1:37 0.5 227 | 5.65 2.0 | 907
1.64 0.6 272 || 5.98 Dill | 953
1.92 0.7 318 6.29 2.2 998 |
2.20 0.8 363 | 6.60 23 | 1043 |
2.47 0.9 408 | 6.91 24 | 1089
2.78 1.0 454 || 7.25 2.5 1134
3.02 1.1 499 7.60 2.6 iLilAs)
3.30 1:2 545 7.93 27 | 1225 |
3.58 13 590 8.28 2.8 1270 |
3.89 1.4 635 8.63 2.9 1315
4.17 15 | 630 9.00 3.0 | 1361 |

|

|
|
|
|
|
|
|

After many days of preliminary experimentation, in which the instrument
was gradually perfected by trial in successive forms before being brought to the
condition to which the foregoing description applies, two days’ experiments were
made on August 27 and 28, and a final series on October 4, 1888. These
are presented in detail in the accompanying tables, and consist of sixty-four
separate experiments made with the plane set vertical and at angles varying
between 5° and 45° with the horizon. The mean temperature is obtained from
thermometer readings at the beginning and end of each set of experiments, which
usually continued from one to two hours. The mean wind velocity is obtained
from the readings of a Casella air meter. The apparatus is so placed upon the
whirling arm that the center of the wind plane is nine meters from the axis of
rotation. One registering sheet serves for a group of observations, consisting in

9
v

18 EXPERIMENTS IN AERODYNAMICS.

general of a succession of settings of the wind plane beginning with a setting at
90° and followed by diminishing angles of elevation. At each setting two obser-
vations are usually obtained by turning the register sheet through an angle of
180°. Thus the two traces made at the same setting should lie in a straight
line passing through the center.

The method adopted in reading the traces is as follows: Straight lines are
drawn through the center and the two traces made at each setting of the plane.
The angle is then measured between the trace of the plane at 90° and the traces
corresponding to other settings. The pressure being normal to the plane, these
measured values should be the complement of the angles of elevation at which
the plane is set. It will be seen by inspection of the accompanying tables that
this relation approximately obtains.

Tables II, II, and IV contain all the original data of the experiments and
their reduction. The first columns require no explanation. The fifth column
(Tables II and IIT) gives the angle measured on the register-sheet between the
radial direction of each trace and the direction of the trace made when the plane
was set vertical. The sixth column gives the measured distance of the trace from
the center, and the seventh gives the results of these extensions converted into

Iz :
ressure on the plane by means of Table I]. The column headed &,, — = contains
P ) = 7

the results of measurements of pressure on the normal plane expressed in terms
of the coefficient %,, of the equation P—k,, V?, in which V is the velocity of the
plane in meters per second and P the pressure on the plane in grammes per square
centimeter, the subscript m being used to designate units of the metric system.

THE RESULTANT PRESSURE RECORDER.

19

Experiments with the Resultant Pressure Recorder to determine the resultant pressure, on a@ square

plane moved through the air with different velocities and different inclinations.

Taste II.—Avueusr 27, 1888.

S. P. Lanciry, Conducting experiments; F. W. Very, Assisting.

Wind plane, 1 foot square (929 square centimeters) ; center of wind plane, ) m. from axis of

rotation; barometer, 736 mm.; temperature at 6 p. m., 21°.0 C.; mean wind velocity, 0.52 meters

per second.

|
|

|
|

Time of observation.

Angle of wind plane

with horizon.

a

Seconds in one reyo-
lution of turn-table.

ter of wind plane.
V (meters per sec.).

Linear velocity of cen-

rection oftrace made |
by plane set at 90°. |

Angle of trace with di-|

Departure of trace |

from center (centi-

meters).

plane. |

on
(grammes per

Pressure

a

2
sq. centimeter).

v]

k, {|

V?

> ——
Py=

0077 V*

3S
Moe
we

40

6:06

6:29

12.65
12.64
12.58
12.67
6.53
6.60
6.55
6.44
6.44
6.43
5.74
5.389
4.87

4.47
4.47
4.49
4.46
8.66
8.57
8.64
8.78
8.78
8.79
9.85
10.50
11.61

1.10
1.05
1.00
0.50
2.80
2.80
2.60
1.65
0.80
0.80
4.10
4.40
4.65

0.195
0.185
0.176
0.088
0.495
0.495
0.465
0.293
0.141
0.441
0.722
0.771
0.820

0.0097
0.0092

0.0067

our

Sh
®

0.80
0.49
0.24
0.24

0.79

20 EXPERIMENTS IN AERODYNAMICS.

Taste II].—Aueusr 28, 1888.
S. P. Laneiry, Conducting experiments ; F. W. Very, Assisting.

Wind plane, 1 foot square (929 square centimeters) ; center of wind plane, 9 m. from axis of
rotation; barometer, 736.6 mm.; temperature, 19°.4 C.; mean wind velocity, 0.37 meters per

second.
5 2) a scoala eee Os al Be

= eS nS Sao | = ge a= as

5 de | 68 | REP] eoSS] 6s 5 i ae

sa | lead ye ale lee Bl caveelel| wyere eno cae | OTT | Pn

: es | 8 | 8,8] e86|/ 28S | 2°

a < RIS 4 =< a) (of

(p. m.)

2:26 GG oe) A262)" tAdSels avers 1.03} 0.180 | 0.0090
90 19:69) Asie 1.00} 0.176] 0.0088
30 12.62 | 448| 65°.8 O70" Onn eee 0.155 | 0.79
15 12.57 | 450] 78 8 OES) Onan ae ee ae 0.156 | 0.72

2:52 90 yal Ic fellee soc 3.25 | 0576} 0.0075
90 (Mav Mente lca 3.15 | 05611 0.0075
45 648| 873| 48 5 3190) || OSo ule eee sss 0587 |) 00
45 6.51 8.69 | 46 0 Siu) exOlpoie cere 0.581 | 0.95
30 G45. Sra ele BOOh VOB oe|e eee. 0592 | 0.90
3 645| 877! 60.5 S00) “566. et eae 0.592 | 0.96
15 643| 879| 75 6 D051! | OSEGi tec eeue 0.595 | 0.61
15 640| 8.84] 76 5 HOON Oda: See 0.602 | 0.57
75| 644| 878| 86.0 145 | O59 es ae ee 0.594 | 044
75| 645| 877| 805 115 I) OQO5u le. eae 0.592 | 0.35

3:40 90 N07 | aes bp 10)! eee 5.40} 0.930 | 0.0074
90 O44) TOSO Nk ovens 450 | 0.786 | 0.0070
45 5.19 | 10.90] 48 .0 BOON) 2 OTODs bere cee 0.915 | 0.77
45 5.29 |. 10.69] 48 .0 A100 || OUD ee nos: 0.880 | 0.82
30 5.26 | 10.75| 60.5 LAGS Otilellice ed 0.890 | 0.87
30 5441), 10401) 50/00) 9 3:90) | rOlGB aN sen ore. 0.833 | 0.82
15 5.09 | 11.11] 81.0 Didnt) SNOW loot 0.950 | 0.44
15 518 | 10.92] 75 5 Doh Ose baos scone 0.918 | 0.42
715) 495| 1142| 84 5 ESOS e028: |b ee 1.004 | 0.28
75| 533| 10.61| 85 5 eA ee O59 eo 0.867 | 0.30

4:30 90 Bion! OUaleneees 3.90 | 0.683] 0.0072
90 Sie QB eee 385 | 0.673 | 0.0070 |
30 553| 10.23| 59 .0 BISb lr (O67Silnaaraee 0.806, 0.84
30 5.56| 1017] 58 8 S160] O64 maces 0.796 | 0.80
75| 541| 1045] 85.0 POO) ROOTS Nee sneee 0.841 | 0.26
75) 809. 1iid |) 475.0 175) AO S198 | ene oee :| 0.950 | 0.33

Remarks.—During these experiments the slight breeze has almost died away ; angle of mean
trace made by plane set at 99° with vertical plumb line drawn on register sheet = 95°.

THE RESULTANT PRESSURE RECORDER 21

Taste [V.—Ocroper 4, 1888.
F. W. Very, Conducting experiments ; Josep LupEwic, Assisting.

Wind plane, 1 foot square (929 square centimeters) ; center of wind plane, 9 m. from axis of
rotation; barometer, 732.3 mm.; temperature 10:15 a. m., 48° F.; 2:30 p. m., 56° F.; mean
temperature, 52° F. = 11°.1 C.; mean wind velocity, 0.85 meters per second.

During these experiments both the velocity of the wind and its direction were quite variable.

SRM icles tle ean Sen re
a aa oH 3S eS 88 aes if =
Pea Sresle= e e es eer SE AS) oy ak ee
eee eee Clee eal ah ee loa Oe Va) By
Pees essence acess
Se | re Ss | Say | B88 | Base
a ra one ae Dw A ON 2
= < De _ =) a
(a. m.)
11:40 15 12.50 4.52 0.5 OMOlsts eee cole Soc 0.155 0.57
10 12.60 4.49 0.5 OHOlss). Vemencae eae 0.154 0.57
10 12.50 4,52 0.5 OVO ac llaieao oedoac 0.155 0.57
(p. m.) 20 12.50 4.52 0.7 Cee Be Siena 0.155 0.79
1:07 20 12.55 4.51 0.6 oe idence oaod 0.154 0.68
90 6.60 8.57 3.0 0.582 0.0073 0.558
90 6.53 8.66 3.0 0.582 0.0071 0.570
1:13 20 6.39 8.85 2.6 O63 Sees tee 0.595 0.78
20 6.48 8.79 2.3 OA0SMile sae oases 0.587 0.70
90 6.48 8.73. 3.0 0.532 0.0070 0.579
90 6.45 8.77 3.0 0.532 0.0069 0.584
1:30 10 6.43 8.79 1.8 (WBE! Nps Saqmon 0.587 0.40
10 6.48 8.79 lef OS03ee eee ee 0.587 0.52
90 6.50 8.70 3.0 0.532 0.0070 0.575
90 i) See 3.2 0.566 0.0074 0.584
15 6.47 8.74 1.5 QOS. Issosescnor 0.581 0.46
15 6.47 8.74 1.9 ee ie" ign ness clooir 0.581 0.59
90 6.45 8.77 3.8 0.664 0.0086 0.584
90 6.57 8.61 3.8 0.664 0.0090 0.563
5 6.48 8.79 1.0 (UG Netacineo ce ¢ 0.587 0.80
1:52 5 6.45 8.77 iil ONO Dies sere rar 0.584 0.33
|

22 PXPERIMENTS IN AFRODYNAMICS.

Collecting the values of #,, from the several days’ observations and reducing
them to acommon mean temperature of 10° C. and pressure of 735 mm., we
have the following summary of results :

km
INGEN Un WMelsbignougsguougcocuoegbnncend9 46 0.00810
€ Ds Pe ay Otros Ocha CORO one 0.00794
October 4o2 oS 232 eRe Oe oe hy ee ioe een 0.00757

The observations of October 4 being of inferior accuracy to the others on
account of the wind, which blew in sudden gusts, the mean of the first two days’
experiments, viz., /,,= 0.0080, may be considered as the final value for the
coefficient of normal pressure resulting from the experiments with this instrument.

The columns headed P,,= 0.0077 V* in the experiments of August 27 and
28, and P,,= 0.0076 V* in the experiments of October 4, give for each obser-
vation of the inclined plane the computed pressure which the plane would
sustain if moving normally with its velocity V. The coéfficient adopted for the
computation is the mean value of £,,, resulting from the experiments of the day.
The last column of the tables contains the ratio of the actual pressure on the
inclined plane to the computed pressure on the normal plane given in the
preceding column.

These ratios from the several days’ experiments are collected in the following
summary, and mean values are taken for the different angles of experiment.
These mean ratios are plotted in Tig. 1, and a smooth curve is drawn to represent
them.

Taste V.—Summary of ratios of pressure on inclined plane to presswre on normal plane.

Tee elaaoe Angles of inclination.
plane (meters }——_———- =a | Remarks.
per sec.). 45° sie 2° 15° 10° 74° Fo |
| S| - z
45 Pale ales3l oeite) 58 aii | satan hall Sere eta * Omit.
| Wl Nsoeboollocegadlo comet + Give one-quarter weight.
| 0.79 68 12 OTT |
oi 11.00 | 0.80 | .78 | 49 | 40 | .24 | .30
1 0'95: | 0:90") 70 62 2 24 Oe
| O97 ley oe EDIT ister Ad
| AAS No oor BD
59 |
11.2 Oye OME) Nee oe.s SO poor | .23. |
POR | WSF lose oc ON lero tat | .80 |
(OS DAR liercire| leescen ons Neeerae es 26 |
OSB. 2, .sc5,c| sonora eseeraaes 83. |
0.80 | |
= | | = ————
Mean....... 0.89 | 0.84 74 55 | 48 | 30 | .31

THE RESULTANT PRESSURE RECORDER. 23

Hig. 1.

Penee aS
aan ae
Saceuae
Cannes
Sanaa

Ratio of the total normal pressure (P.) on an inclined square plane to the pressure (P,,) on
a normal plane, the planes moving in the air with the same velocity.

5

Abscissee. Angles of inclination («) of plane to horizon.
: 1 + , .
Ordinates. pt (a) (expressed as a percentage).
90
© Represents the mean of observed points for each angle of experiment.

24 EXPERIMENTS IN AERODYNAMICS.

The values in the tables are subject to a correction resulting from a flexure
in the balance-arm and its support. It was observed (see note in Table II1)
that the trace of the plane set at 96° did not coincide with the horizontal (7. e.,
the perpendicular to the vertical) line marked on the trace, but was uniformly 4°
or 5° below it; so that the angle between the vertical and the trace of the plane
did not measure 90°, as had been assumed, but uniformly 94° or 95°, the average
being 94°.6. This result was found to be due to the bending backward of the
balance-arm and its support by the pressure of the wind, while the recording
board and plumb-line presented only a thin edge to the wind, and consequently
remained relatively fixed. During motion, therefore, the plane actually had an
inclination to the horizon about 5° greater than the angle at which it was set when
at rest. This flexure seemed to obtain for all angles of experiment, but with
indications of a slightly diminishing effect for the smaller ones; consequently
the pressure ratios above given for angles of 45°, 30°, 20°, etc., really apply to
angles of about 50°, 35°, 25°, ete. After making this correction the final result of
the experiments is embodied in the line of Fig. 1 designated “ corrected curve.” *

At the inception of the experiments with this apparatus it was recognized
that the Newtonian law,+ which made the pressure of a moving fluid on an
inclined surface proportional to the square of the sine of the angle between the
surface and the current, is widely erroneous, though it is still met in articles
relating to fluid pressures, and vitiates the results of many investigations that

* The ratios given by the “corrected curve” of the diagram have been tabulated for angles of every 5° and
then compared with all the experiments and formulze with which I am acquainted. Only since making these
experiments my attention has been called to a close agreement of my curve with the formula of Duchemin,
whose valuable memoir published by the French War Department, Mémorial de Tl Artillerie No. V,1 regret not
knowing earlier. The following table presents my values, the values given by Duchemin’s formula, and a column
of differences :

Ratio of the total pressure (Pa ) on an inclined square plane to the pressure (Py) on a normal
plane moved in the air with the same velocity.

Pa .
pe wAeven by—
Angles of inclination |- = ieee
of plane to direc- Vu | Difference: Duche-
tion of motion. Experiments with Duchemin’s formula: min—Langley.
(@) | Resultant Pres- | 2 sin a
sure Recorder. 1+ sinta
5° 15 17 + .02
10 30 4 O04
15 AG 48 02
20 60 61 01
25 agit fe OL
30 78 80 02
35 54 86 02
40 89 OL 02
45 93 94 OL

{Implicitly contained in the Principia, Prop. XX XIV, Book IT.

THE RESULTANT PRESSURE RECORDER. 25

would otherwise be valuable. Occasional experiments have been made since the
time of Newton to ascertain the ratio of the pressure upon a plane inclined at
various angles to that upon a normal plane, but the published results exhibit
extremely wide discordance, and a series of experiments upon this problem
seemed, therefore, to be necessary before taking up some newer lines of inquiry.

The apparatus with which the present experiments were made, was designed
to give approximations to the quantitative pressures, rather than as an instru-
ment of precision, and its results are not expected to afford a very accurate
determination of the law according to which the pressure varies with the angle
of inclination of the surface to the current, but incidentally the experiments
furnish data for discriminating between the conflicting figures and formule that
now comprise the literature of the subject. We may remark that they incident-
ally show that the effect of the air friction is wholly insensible in such experi-
ments as these; but the principal deduction from them is that the sustaining
pressure of the air on a plane 1 foot square, moving at a small angle of inclina-
tion to a horizontal path, is many times greater than would result from the
formula implicitly given by Newton. Thus for an angle of 5° this theoretical
vertical pressure would be sin® 5°cos 5° = 0.0076 of the pressure on a normal
plane moving with the same velocity, while according to these experiments it is
in reality 0.15 of that pressure, or twenty times as great as the theoretical amount.

CHAPTER V.
THE PLANE-DROPPER.

It is so natural to suppose that to a body falling in the air under the
influence of gravity, it is indifferent whether a lateral motion is impressed upon
it or not, as regards the time of its fall, that we may sometimes find in elemen-
tary text-books the statement that if a ball be shot from a cannon horizontally,
at any given height above the ground, and if a ball be dropped vertically at the
same instant with the discharge, the two projectiles will reach the ground at the
same time, and like illustrations of a supposed fact which has in reality no
justification in experience. According to the experiments I am about to describe,
this cannot be the ease, although it requires another form of projectile to make
the difference in the time of fall obvious.

It is shown by the following experiments that if a thin material plane be
projected in its own plane horizontally, it will have a most conspicuously different
time of falling according to the velocity of its lateral translation; and this time
may be so great that it will appear to settle slowly down through the air, as it
might do if almost deprived of weight, or as if the air were a highly viscous
medium, the time of fall being (it will be observed) thus prolonged, when there
is no inclination of the plane to the horizon—a noteworthy and unfamiliar fact,*
which is stated here on the ground of demonstrative experiment. The experi-
mental quantitative demonstration of this important fact, is the primary object
of the instrument I am about to describe, used with the horizontal plane. It is,
of course, an entirely familiar observation that we can support an inclined plane
by moving it laterally deriving our support in this case from the upward com-

* An analogous phenomenon concerning the movement of one solid over another yielding one, such as when
“Swift Camilla scours the plain,
“lies o’er the unbending corn, and skims along the main ;”
or in the familiar illustration of the skater on thin ice, or in the behavior of missiles like the boomerang, has
long been observed; and yet, remarkable as its consequences may be, these seem to have attracted but little
attention. Neither has the analogy which it is at least possible may exist between this familiar action of the skater
upon the ice and of the potential flying-machine in the air been generally observed till lately, if at all—at least,
so far as I know, the first person who has seemed to observe the pregnant importance of the illustration is
Mr. Wenham, whom I have already alluded to. I do not, then, present the statement in the text as a fact in
itself unpredictable from experience, for it is a familiar fact that the air, like every material body, must possess
inertia in some degree. It is the quantitative demonstration of the extraordinary result of this inertia which
can be obtained with simple means in causing the thin air to support objects a thousand times denser than
itself, which I understand to be at the time I write, both unfamiliar in itself, and novel in its here shown con-

sequences.

(26)

THE PLANE-DROPPER. 27

ponent of pressure derived from the wind of advance; but, so far as I am now
aware, this problem of the velocity of fall of a horizontal plane moving hori-
zontally in the air has never been worked out theoretically or determined experi-
mentally, and I believe that the experimental investigation whose results I am
now to present is new.

With all the considerations above noted in view, I have devised a piece of
apparatus which, for distinction, I will here call the Plane- Dropper, intended, in
the first place, to show that a horizontal plane in lateral motion requires an
increased time for its descent ; second, to make actual measurement of the time
of fall of variously shaped planes and to give at least the first approach to the
procuring of the quantitative data; third, to connect these experiments with those
immediately allied to them, where the plane has an inclination to the horizon ;
and, fourth, to make experiments to show the depth of the air strata disturbed by
the moving plane during the time of its passage.

Drawings of the Plane- Dropper are given in plate VI. F is a vertical iron
frame with a wooden back WW, which is shown fastened by bolts B to the
end of the arm of the turn-table. The fourth side of the rectangle is a planed
brass frame on which an aluminum falling-piece runs up and down on friction
rollers. The plate contains enlarged front and side views of the falling-piece,
and a section of the brass frame and falling-piece, showing the arrangement of
the ebonite friction rollers. By means of the clamps CC’ the falling-piece carries
two wooden planes, which may be set by the clamps DD’ horizontal, or at any
angle with the horizon up to 45°. Guy lines extend from the top and bottom of
the falling-piece to the outer edges of the planes and keep them from bending.
A detent at the top of the frame holds the falling-piece until released at any
desired instant by the action of an electro-magnet, M. A spring cushion, 5, at
the bottom of the frame, breaks the force of the fall.

Provision is made for setting the brass frame vertical, and by means of the
handle H the frame can be revolved 180° about its vertical axis, so as to present
successively one side or the other side to the wind of advance, and thus to eliminate
any defect in setting the wings absolutely horizontal, or any inequality in the
instrument not otherwise suspected.

The total fall is four feet, and the total time of fall is registered electrically
by means of contact-pieces @ and e, near the top and bottom of the frame. As
soon as released, the aluminum falling-piece presses the contact-piece @ against
the frame and completes the circuit. While falling, the circuit is open, and at
the distance of four feet the contact-piece e is pressed against the frame and the
circuit is again closed. In November, 1890, three additional contact-pieces,
b, c, d, were added, so as to measure the time of fall through each successive foot.
The registration is made on the stationary chronograph, together with that of

28 EXPERIMENTS IN AERODYNAMICS.

the quadrant contacts of the turn-table, the currents for the moment being cut
off from the quadrant contacts and sent through the Plane- Dropper.
The dimensions and weight of the principal parts of the apparatus are as

follows:

Ibeyaveqley Oe lores: blo occ Dopoo sooo SES CUD OcESDOCoGOoNDoCOOOES 160 centimeters.
eneth of ‘aluminium falling-piecer oer. a. creleiele)<leletlel-)iielielelerer= 25
henethvots DUTerS em eesiser sete ete eee eet nena 5
Actual distance of fall (between contacts)....................-- 122
Distance of center of brass frame and falling-piece from center of

(Lon VHT Paonia loaanaanocscoossconApoOONSe4seucac 981 sf
Wieiehtron tallimg=piecetmr smite eee ist iatesttotr ities 350 grammes.

The planes are made of varnished pine about 23mm. thick, and stiffened on
one edge with an aluminum strip.

Five different pairs were used, having the following dimensions and
weights :

(1) Two planes, each *6 x 12 in. (15.2 x 30.5 em.); weight of pair, 123 grammes.
C2)p nse if Se 8 nna (2279s 2 03 rcms) es se alas) <¢
C) ee s “ 12x 6 in. (05x 15.2 cm.) ; ee Sop rill 4: s
eye : “ 18x 4in. (445.7x 10.2 em.); ss “ 114 «
©) ss “15x 4 in. (88.1 x 10.2 cm.); bela i

Each pair of planes, therefore, except the last, has an area of one square
foot, and weighs, with the aluminum falling-piece, approximately one pound.

It may be desirable to add that this instrument was constructed with special
pains in all the circumstances of its mechanical execution, the very light falling-
piece, for instance, moving on its friction wheels so readily that it was not
possible to hold the rod in the hands sufficiently horizontal to keep the “ falling-
piece”? from moving to one end or the other, like the bubble of a level held in
the same manner.

Preliminary experiments were made to determine the effects of friction on
the time of fall, when the Plane- Dropper is in rapid horizontal motion, by drop-
ping the aluminum falling-piece without planes attached, and it was found that
under these circumstances the time of fall is not sensibly greater when in rapid
motion than when at rest. As a further test, the planes were then attached to
the falling-piece in a vertical position, that is, so as to present their entire surface
to the wind of rotation, and thus to produce a friction very much greater than any
occurring in the subsequent experiments; but the time of fall was not increased
to any notable degree. The effect of friction and other instrumental errors are
shown thus, and by considerations already presented, to be negligible in com-
parison with the irregularities inevitably introduced by irregular air currents

* First measurement refers to advancing edge.

THE PLANK-DROPPER. 29

when the whirling table is in motion, which appear in the observations, The
probable error of the measured time of falling in still air, when only instrumental
errors are present, is within z}¢ of a second.

The first series of experiments with horizontal planes was made May 25
and June 10 to June 14, 1889, and was devoted to the first two objects already
set forth, namely:

1st. To show by the increased time of fall that the supporting power of the
air inereases with the horizontal velocity cf the body; and,

2d. To get first approximations to the times of falling of rectangular planes of
different shapes and aspects, the latter condition having reference to whether the
long or the short side of the rectangle is perpendicular to the direction of advance.

An abstract of the note book for June 11, 1889, is given here as an example
of the detailed records made in these experiments.

June 11, 1889.—S. P. Lanciny, Conducting experiments and recording ; F. W. Very, Assisting.

Notes: “A” and “ B” designate the direct and reversed positions of the brass frame and falling

piece; belt on third pulley.
To determine time of falling.

sie 20
Ss 2 =
os =.
oka ee)
e : ; 4's 3 ig
Size and attitude of planes. ane oS 3
OSG et)
SA S)
2s RE
as |
<a S
18 x 4-inch planes, horizontal. .... 3.8 A 1.50
3.8 A 1.15
3.75 B 1.20
4.25 B 1.15
12 x 6-inch planes, horizontal: |
Ati NESt| CMO PEDsAM) ye eller 0.52
e 6 Ue) SPB oe nee ie ee iia on: 0.52
. ag eee eee eee 0,52
a ee OU ie Sacto ial ctor mint ier | 0.54
In motion on turn-table .... GOP Biowa
4 ee eS occe 6.2 B 0.80
ce se oy cee 61 | A076
¥ s oe ore 6.1 | A 0.80
i : 3.5 A 1.00

The detailed observations with the five different planes already described
are contained in Tables VI and VII, and the results are presented graphically
in figure 2, where the times of fall are plotted as ordinates, and abscissse are
horizontal velocities of translation.

30 EXPERIMENTS IN AERODYNAMICS.
Taste VI—May 25, 1889.
To find the time of fall of different planes ; plane-dropper statioua;y.
S. P. Lanciry, Conducting experiments ; F. W. Very, Assisting.

Earometer, 731.5 mm.; temperature, 17°.5 C.; wind, light.

| Weight (with dropping piece). Time of fall of

teeta eee | _| Angle with | 4 feet (1.22
nee 1b Bee: horizon. | — meters).

| (Grammes.) | (Pounds.) (Seconds. )

One pair 12 x 6 inches (50.5 x 15,2 464 1.02 0° 0.58
cm.). 0 0.58
12 i2 0 0.52
S ee ls 45 0.54
7P 72 | 45 0.55

One pair 18 x 4 inches (45.7 x 10.2 | 464 1.02 0 0.54
cm.). | 0 0.55
45 0.55

Result: The time of fall of both planes, at angles both of 0° and 45°, is, approximately, 0.55

seconds.
Taste VII—June 10, 11, 12, ann 14, 1889.

S. P. Lanctey, Conducting experiments ; F. W. Very, Assisting.

Mean barometer, 734.0 mm.; mean temperature, June 10, 26.6° C.; June 11, 17.8° C.; June 12,
Dilete Ch une lA. 2ouos Cs

To determine the times of fall of horizontal planes endowed with Us bead wh ee ny ee ee
Lemmamnelien at which inclined planes are sup-
ported by the air.
' 1 . 1 ; 1 ' | ' 1 a ' +
g a a o és Ww el pee =I Re
Dimensions and aspect Wate Bie oe || eye piae oe! Dee ee |S BAD LE Dy
of plane. | 682 | 888 | o6 = cee lees
et ot S S TS N 3
= es a | |< |& se
1889. | | 1889. |
13 18 June 10 | 0.00 0.0 | 0.53 || June 10} 16° 51 12.1
> x | x 5.70 10.8 | 0.70 2 5 5.4 18.1
Is 18 We 5.90 | 104 0.65
3 3.35 | 184 | 1.62 |
18 x 4 inches (45.7 x 10.2 - 3.45 ied, 1.65
cm.). | “ 5.80 10.6 0.85
Weight, 1.02 lbs. (464 | a 4.35 14.2 | 0.90
grammes). 3.10 16.4 1.08
Radius of rotation tocen- | June 11 3.80 16.2 1.30 || Junell | 20° | 6.0 10.5
ter of planes, 9.81 m. | :: | 3.80 16.2 | 1.15 | e 15 6.2 9.9

THE PLANE-DROPPER.

Taste VII—Continued.

dl

oam| os ¢ e |oaq|e8
ey tae = 2 2S) |] ce fe
eevae aSS [qs | ee | wa | 288 | qs.
Dimensions and aspect | pat. | > ~@ Oa See Dees Sees es
of plane. Ss) el opal axehieul is. 5 Bless | aha
oer iS — © meermtGd 8 S)
a5'3 | EES | ‘ | go's | BES
Sree om 7 is| | cI aie Om
= ss a < | ss
| |
1889. | | _ 1889. |
18 13 Aiwragyilil || Biyis 164 | 1.20) June ll | 34) 33 18.7
* + < 4.25 14.5 1.15
78 78 | June 12 3.00 20.5 1.95 | June12) 3 3.09 18.4
“ 3.60 ffl 1.50 #8 2.85 21.6
18 x 4 inches (45.7 x 10.2 “ 3.00 205m ee 557
em.). x 3.05 20.2 2.68 |
Weight, 1.02 Ibs. (464 « 3.10 19.9 | 2.75 ||
erammes). = 3.15 TIBHS |) P05 |
ie 3.70 16.8 1.65
12 12 “ 0.00 0.0 | 0.56 || June 11 | 25° 5.6 11.0
-— +E f Gil5- | 1010) 1 0:80:|| 1 # 6 3.8 16.2
iz 72 ‘ 6.05 10.2 | 0.74 | June 12 | 5 3.0 18.7
June 11 3.50 17-6) 21.00) |
12x 6 inches (30.5 x 15.2 ge 3.40 ies | alg)
em.) June 12 2.87 21.4 1.29 |
Weight, 464 grammes. a 2.82 ZANE) fp a1)
EI | Re cotsaobari 0.0 | 0.57 | 25° 6.0 10.3
“ 13.15 47 | 0.62 | we 15 49 12.6
a SO ek 6.5| Oval ae 12 4.2 14.7
s 2.85 21.6 | 0:82) | e 6 2.9 21.2
2.65 23:3) | (0:86) |
ee he ey oot 0.0 | O57 || « 30° 5.9 10.5
S | 11.65 2 | 0.58 | s 20 5.0 12.3
« 4.10 15.0 0.65 | ie 15 4.2 14.7
x 5.10 TO || (OLR) | : 3 3.8 16.2
se 2.78 22.2 0.72 os 9 2.9 21.2
6 x 12 inches. |
Weight, 473 grammes. I
15 15 June 14 5.65 10.9 0.76 || June 14 | 20° 5.25 alee
“ne | SiO 199° 08 || “is | eto | 12K
15 Is 3 3.00 20.5 1.28) | e 15 4.65 13.3
‘v3 A BA 9
15 x 4 inches (38.1 x 10.2 | 10 eds | Tale
2 ( 3.59 16.0
_cm.). | 5 3.30 18.7
Weight, 468 grammes. 4 210 19.9
| |

32 EXPERIMENTS IN AERODYNAMICS.

lives, +

125

100

Diagram a Plane.
peer | ee

0.75

Times of falling 4 feet of horizontal planes on the Plane-Dropper.
Average weight of planes = 465 grammes.

Abscissee : = Horizontal velocities of translation in meters per second.
Ordinates : = Times of fall in seconds.

THE PLANE-DROPPER. 33

Perhaps the most important primary fact exhibited by these experiments
is that the time of fall for horizontal planes of all shapes is greater as tho
horizontal velocity increases, and also (as the form of the curves shows) that this
retardation in the velocity of falling goes on at an increasing rate with
increasing velocities of translation.

Secondly, we see that those planes whose width from front to back is small
in comparison with the length of the advancing edge have a greater time of
fall than others. This difference is uniform and progressive from the 6 x 12
inch planes to the 18 x 4inch planes. Expressing this advantage quantitatively,
the curves show that the planes having an advancing edge of 6 inches and
a width of 12 inches from front to back, when they have a horizontal velocity
of 20 meters per second, fall the distance of 4 feet in 0.7 second, while planes
of the same area and weight having the advancing edge 18 inches and 4 inches
from front to back, when moving with the same velocity, are upheld to such an
extent that their time of fall is 2 seconds. This interesting comparative result is
also indirectly valuable in giving additional evidence that the largely increased
time of fall of the better-shaped planes at the high speeds is not due to the lateral
friction of the falling-piece against the frame. The friction with the 6 x 12 inch
planes is as great as with any of the others, yet their time of falling is only
slightly greater at high speeds than at rest. Attention is called to the fact that
at the highest velocity attained in the present series of experiments, 20 meters
per second, the curve shows that the time of falling of the 18 x 4 inch planes was
increasing very rapidly, so much so as to make it a subject of regret that the
slipping of belts prevented experiments at still higher speeds. We may, however,
reasonably infer that with a sufficient horizontal velocity, the time of fall may be
prolonged to any assigned extent, and that for an infinite velocity of translation,
the time of fall will be infinite, or, in other words, that the air will act as a solid
support.

In may be of interest to connect these observations with some partly analogous
facts which are more familiar.

It is frequently observed that a sheet of very thin ice will bear up a skater
if he is in rapid motion which would not sustain his weight if he were still; and
even if we neglect the slight difference of specifie gravity between water and
ice, and suppose the latter to have no differential buoyancy, the rapid skater
will still be able to pass safely over ice that would not bear his weight if he
were at rest; for while his mass is the same in both eases, that of the ice called
into play in sustaining him is only that corresponding to one unit of area when
he is at rest, but to many when he is moving.

In this form of explanation and illustration the attention is directed only to
the action of the air beneath the plane, but in fact the behavior of the air above

5

34 EXPERIMENTS IN AERODYNAMICS.

the plane is of perhaps equal importance, and its action has been present to my
mind throughout these experiments, although for the purpose of concise exposition
only the former is here referred to. By analogous reasoning in the case of a
heavy body immersed in any continuous fluid, even gaseous, while the mass
of air or gas whose inertia is called into action is small and affords a slight
sustaining power when the body is at rest, it becomes greatly multiplied with
lateral motion, and the more rapid this lateral motion, the greater will be the
sustaining action of the fluid. So, then, in the case of any heavy body which
will fall rapidly in the air if it fall from rest, the velocity of fall will be more
and more slow if the body be given successively increasing velocities of lateral
translation and caused to run (so to speak) upon fresh masses of air, resting but
a moment upon each.

The above analogy, in spite of its insufficiency as regards the effect of elas-
ticity, is useful, and may be further extended to illustrate the relative results
obtained with the differently shaped planes and with the same plane under
different “aspects ;” thus the action on the air of a plane whose advancing edge
is twice its lateral edge—e. g., the 12x 6 inch plane, with 12-inch side foremost—
may be compared to that of two skaters side by side, each advancing over his own
lines of undisturbed ice; but the same plane with the 6-inch side foremost, to the
same skaters, when one is behind the other, so that the second is passing over ice
which has already yielded to the first and is partly sinking.

The second series of experiments, made on the same dates as the first, was to
cover the third object of experiment—that is, to determine for different angles of
inclination what speed is necessary in order to derive an upward thrust just
sufficient for sustaining the planes.

The results of these two series of experiments furnish all that is needed to
completely elucidate the proposition that I first illustrated by the suspended
plane, namely, that the effort required to support a bird or flying machine in the
air is greatest when it is at rest relatively to the air, and diminishes with the
horizontal speed which it attains, and to demonstrate and illustrate the truth of
the important statement that in actual horizontal flight it costs absolutely less
power to maintain a high velocity than a lowone. It has already been explained
that when the planes have such an angle of elevation and such a horizontal
velocity that they first rise from their support and are then with a slightly
diminished velocity just sustained without falling, they are said to “soar,” and
the corresponding horizontal velocity is called “soaring speed.” Attention has
already been called to the importance thus attachable to the word “ horizontal”
as qualifying flight, and implying its most economic conditions, when no useless
work is expended.

THE PLANE-DROPPER. 35

The actual mode of experiment with the inclined planes was to set the plane
at a given angle of elevation, for example 5°, and approximate to the critical
soaring speed by gradual variations of velocity, both above and below it. The
following extract from the note book shows the character of the record made in
executing this experiment :

12x 6 inch planes, inclined.

Time of 1 revolution
Angle of inclination. of turn-table Attitude of plane.
(seconds).
25° 5.6 Soaring.
6 3.8 -

18 x 4 inch planes, inclined.

3 SiG
S BES
re
a Sieh
Ss iS
ad “3 8
ws O ees Attitude of plane. Estimated result.
o:5 (eo) 2 PS
o =
= S23
a EES
< ima
|
4° 3.4 More than soaring............- ( For angle 33°, soaring speed = 1 rev-
3 3.2 Not quite soaring............-. {olution in 3.3 seconds.
20 6.0 Soaring.
15 5.5 More than soaring......-...-.- { For angle 15°, soaring speed = 1 rev-
15 6.8 Not quite soaring...........-- |{ olution in 6.2 seconds.

The detailed observations have already been given in Tables VI and VII
and the results are plotted in Figure 3, in which the ordinates are soaring speeds
and the abscissse are the corresponding angles of inclination of the planes to the
horizon. This diagram shows that when set at an angle of 9° the 6 x 12 inch
plane requires a horizontal velocity of 21.2 meters per second to sustain it in the
air, while the 18 x 4 inch plane, set at the same angles, is supported by the air
when it is driven at a velocity of only 14 meters per second. The work to be
done in maintaining the flight at 14 meters per second is less than one-half that
for 21.2 meters per second, the angle remaining the same.

These experiments enable us to make a first computation of the work expended
in horizontal flight. Let us, then, determine the horse-power required to drive
the two 18 x 4 inch planes horizontally in the air, when the planes are inclined
successively at 9° and at 5°. The work done per second is given by the product
RV, RB being the horizontal component of pressure on the plane, and V the

36 EXPERIMENTS IN AERODYNAMICS.

Velocities of soaring of inclined planes on the Plane-Dropper.

Average weight of plane = 465 grammes.
Abscisse : = Angles of inclination (a) of plane to horizon.
Ordinates : = Velocities in meters per second.

THE PLANE-DROPPER. 37

soaring speed. From Fig. 3 we find that the soaring velocities corresponding
to these angles are respectively 14 and 17.2 meters per second.
Taking the vertical component of pressure as equal to the weight of the plane,

464 grammes, which relation obtains at soaring speed, the horizontal component
of pressure, or the resistance to advance, is given by the formula :

R= 464 tan 9° = 73.3 grammes, for 9°;

R= 464 tan 5° = 40.6 grammes, for 5°,
a formula which is immediately derived from the fundamental principles of
mechanics and appears to involve no assumption whatever. The work done per
minute, R < V, is 62 kilogrammeters (450 foot-pounds) for 9°, and 43 kilogram-
meters (312 foot-pounds) for 5°. For the former case this is 0.0156 horse-power,
and for the latter case, approximately 0.0095 horse-power ; that is, less power is

IniGaAs

Times of falling 4 feet of single and double pairs of 15 x 4 inch planes.

Abscissee: Horizontal velocities of translation in meters per second.

Ordinates: Time of fall in seconds.
required to maintain a horizontal velocity of 17 meters per second than of 14; a
conclusion which is in accordance with all the other observations and the general
fact deducible from them, that it costs less power in this case to maintain a high
speed than a low one—a conclusion, it need hardly be said, of the very highest
importance, and which will receive later independent confirmation.

Of subordinate, but still of very great, interest is the fact that if a larger
plane have the supporting properties of this model, or if we use a system of
planes like the model, less than one-horse power is required both to support in
the air a plane or system of planes weighing 100 pounds, and at the same time
to propel it horizontally at a velocity of nearly 40 miles an hour.

38 EXPERIMENTS IN AERODYNAMICS.

The third series of experiments made with the plane-dropper is designed
to investigate the effect of two sets of planes, one above the other. For this
purpose the planes and falling piece are so weighted that the previous ratio of
weight to surface is retained; that is, in the previous case the weight is 1 pound
to 1 square foot of surface, and with the double set of planes the weight is

Experiments with two sets of planes, one above the other.

Taste VIIL—June 14, 1889.

To determine the times of fall of a system of horizontal planes ee uf ee eda eee ee ae
lowed with horizontal velocity. etic) Blemnoy arualaned aries
Cane Y be supported by the air.
fd . 1 oy 1 ¢q mo -
: 22 2 S S & 5 ES Horizontal velocity.
eo eee eee eae s apes :
Ono | 0 an] & Su O 5 mE
Dimensi Jaspect of plane.| 8° | SSG (Se /Su| ole) eS ay
imensions and aspect of plane.| © (2 | B25) 0S |S CA a eS
BO | OSA OAC aes CS) 88 26
asiie, || AS Sos || S = of2 2 25
f28) | S328 a gS | 2s a
a a B& |< |& S S
io _' __18 3.1 19.9 | 0.90} 10° | 4383 | 142 46.7
ies 11 a S| 8 3.85 16.0 52.5
te || 263 :
6 3.48 He 58.1
15 x 4 inches (88.1 x 10.2 cm.). 6 3.89 18.4 60.3
Double pair of planes, 2 inches 5 Did not} rise.
(5.1 em.) apart.
Total weight of planes and falling-
piece, 942 grammes.
Same planes, 4 inches (10.2 em.) 7.30 8.4 0.738 )15 | ITL(S) 38.1
apart. 3.15 ONT 1.36 | 10 13.3 43.5
10 13.3 3.5
ft 18.2 59.8
5 18.5 60.7
4 18.5 60.7
4 18.9 61.8
| | |
Same planes, 6 inches (15.2 em.) 5.88 10.5 0.73 | 20(2)| 5.60 11.0 36.1
apart. 2.78 22.2 1.34 | 15 5.40 11.4 37.
0.00 0.0 | 0.55 | 10 4.55 13.5 44.4
2.65 23.3 LEGO a 3.95 15.6 51.2
5 3.45 17.9 58.6
5 3.45 alga) 58.6
4 2.93 21.0 69.0
4 2.95 20.9 68.5
23 2.85 21.6 71.0

made 2 pounds to 2 square feet. The preceding experiments, made with the
single pair of 15 x 4 inch planes, were then repeated on June 14, with a double
pair of planes placed at distances of 2, 4, and 6 inches apart. The detailed
observations are given in Table VIII. The times of falling are plotted in Fig. 4.
The soaring speeds are plotted in Fig. 5, without attempting to smooth out the

THE PLANE-DROPPER. 39

oc Veena ae ae ee :
| A

Be: -

perSecond. |
per Second.

Metres
Feet

Ss
D>
N
(JS)
on

Velocities of soaring of single and double pairs of 15 x 4 inch inclined
planes on the Plane-Dropper.

Abscisse : = Angles of inclination (2) of plane to horizon.

Ordinates : — Velocities in meters per second and feet per second.

40 EXPERIMENTS IN AERODYNAMICS.

inaccuracies of observation. The general result presented by both the falling
and soaring planes is that when the double pairs of planes are placed 4 inches
apart, or more, they do not interfere with each other, and the sustaining power
is, therefore, sensibly double that of the single pair of planes; but when placed
2 inches apart, there is a very perceptible diminution of sustaining power shown
in the higher velocity required for support and in the greater rapidity of fall.
Manifestly, however, this result can hold good only above some minimum
velocity of translation, and, in general, we may say that the closeness with
which the planes can be set without producing any diminution of sustaining
efficiency is a function of the velocity of translation, so that the higher the velocity,
the greater the proximity. It was desired, therefore, to ascertain the minimum
velocity for which the preceding conclusion holds good, namely, that planes 4
inches wide do not suffer any loss of sustaining power if placed one above the
other and 4 inches apart. Experiments with these double pairs of planes were,
therefore, continued on August 22, 23, and 24 for the purpose of getting these
data. The same planes were used and were placed at the same distance apart,
viz., 2, 4, and 6 inches, and a set of experiments was also made with the single
pair. Previous to these experiments at high speeds the Plane- Dropper was
stiffened in order better to preserve its verticality under strong wind pressures,
and precaution was taken to observe how closely this condition was maintained.
The new observations were somewhat different from the early ones, and consisted
in measuring the time of fall of the double planes—i. ¢., one over the other when
set at different angles ranging from — 7° to + 7° at three different velocities, viz.,
23.5, 13.0, and 6.5 meters per second. For every setting the brass frame was
turned on its pivot through an angle of 180°, so as to present first one side then
the opposite as the advancing face. The two positions are designated by A and
B in the accompanying Tables, IX, X, and XI, which contain 125 separate
observations at the above-named different velocities, angles, and settings.

THE PLANE-DROPPER. 41

Experiments to determine the time of falling of two sets of planes, one above the other (second series).
Taste IX.—Aveusr 22, 1889.
F. W. Very, Conducting experiments.

Barometer, 781.8 mm.; mean temperature, 23°.9 C.; wind, light.

80 4 S4A| O8 !
Pe |e ee Sale lg
Fate «| one tetaee auld Pa Reon
SS 4 . awe OS oS eS
Dimensions and aspect of 68 | 36 & . a S g es sas RES
planes. 5 & =) 05 2 BES ora
Be eS Desise) |S on |e
B ey SS | esta |S
ee ees ss =
|
nS a . CPM eta once. 0.69
E| i Opniitee set 0.62
(os ee A 0 2.60 ( 1.68
B 0 2.65 a 1.70
15 x 4 inches (88.1 x 10.2 B 0 2.60 3.7 1.70
cm.). B |—2 2.65 3.3 0.70
Double pair of planes. 4 eae = 2.65 23.3 1.00
inches apart. A |—5 2.60 23.7 0.75
Total weight, 942 grammes. | A | —5 2.50 24.6 | 0.50
A |+1 2.50 24.6 2.20 | Fell, then soared.
A |+1 2.65 23.3 | 6.15 | Fell slowly.
B |—1 2.65 23.3 | 0.90
B |--1 2.65 23.3 | 1.20
Same planes, 2inchesapart. | A 0° 2.39 26.2 1.60
B 0 2.45 25.1 1.20
Psaes 0 2.60 23.7 1.90
B 0 2.60 23.7 1.30
A 2, 2.95 20.9 | 4.15 | Soared, then fell.
B |—2 2.75 22.4 | 0.70
A | +2 2.70 22.8 | 5.80 | Gradual fall, but very slow.
B |—2 2.65 23.38 | 0.72
A 5 2.60 TN lbsoe a Stayed at top.
B |—8 2.65 WR) || Oba
B /|—8 2.75 22.4 | 0.50
Same planes, 6inches apart. | A Of 3.30 18.7 1g
B 0 3.30 18.7 | 1.20
A 0 3.35 18.4 | 1.50
B 0 3.30 18.7 1.30
A |+1 3.00 20.5 |14.80 | Fell very slowly.
B |—1 2.95 20.9 | 1.00
A |+1 3.00 90.5 |14.20 | Fell very slowly.
B |}—1 3.00, 20.5 1.10
B |—3 3.15 19.6 | 0.75
B = D 3.20 19:2 0.75
|

Result: It is certain that any angle greater than + 1° (with planes 6 inches apart) would
produce soaring, and as the error of verticality in this day’s observations probably does not
exceed 1° during motion, we may take about 2° as the soaring angle for the speeds used.

42 EXPERIMENTS IN

Barometer,

52.5 mm.; mean temperature,

y)

AERODYNAMICS.

TABLE X.—Aveust 23, 1889.

2°.8 C.; wind, light.

lution of turn-
table (seconds).

ity GQneters per

Ep S 2 2
Dimensions and aspect of | 2s = 5 5 & ey)| es Rarmitke
planes. | Be 3 | Bieshiel || 155
3 = a) S58 | o
| a 2 S esta
& |< |e Fa =
15 15 NE Oa. ESO 7.9 | 0.80
x Hi IE \* B | 0 9.30 6.6 0.70
ww | 5 A 0} 9.10 6.8 | 0.70
B 0] 8465 7.3 | 0.65
15x 4 inches (88.1 x 10.2} A 0 4.80 12.8 1.08
em.). B 0 4.80 12.8 1.02
Double pair of planes, 6 A 0} 4.85 12.7 0.90
inches apart. B 0 5:00, 12.3 1.20
Total weight, 942 grammes. ea 5) 4.95 12.4 1.55
| A |+ 5) 10.05 6.1 0.70
13) || 3 Bl) 315) 6.6 | 0.60
By = |) Zon) 13.1 | 0.64
By Woe S|] atau 13:0 | 2:10
Bion 200 6.8 | 0.78
IN = 5) || SII TB | OURS
INO =) |) cles) 13.0 | 0.70
IN Wop if |} asta) 12.7 111.15
IN War qe | sH2X0) 7.5 | 0.90
1 9.35 6.6 | 0.62
1 j= | Er) 13.1 0.58
B |+ 7) 470 13.1 7.25
Is oe cd i Sako) 6.8 | 0.80
i | S510 6.5 | 0.60
Aa ier (ia eed 13.0 | 0.57
A |+10} 4.65 IRS loco 05 Soars.
A 10 7.90 7.8 1.10
B 10 | 10.25 6.0 | 0.75
Same planes, 4 inches apart. A 0°) 11.55 5.3 | 0.62
B 0 8.60 7.2 0.60
A 0 4.60 13.4 0.95
B 0} 4.70 13.1 | 0.89
B |+ 5 10.10 6.1 0.69
B |}+ 5 4.70 13.1 2.50
A |— 5| 4.70 13.1 0.70
A |— 5 | 10.20 6.0 0.65
A |+ 5} 7.65 8.1 | 0.63
A |+ 5| 4.70 13.1 2.90
B |— 5 4.80 12.8 0.59
B |— 51 10.50 5.9 0.59
A |+ 7] 18.70 4.5 0.59
A |+ 7] 4.85 12.7 | 3.07
B |—7| 487 12.7 | 0.58

THE PLANE-DROPPER. 43

TABLE X.—Avususr 23, 1889—Continued.
Bah los opines ale es 2
= & Sy BITS) || ox ce,
[Pees eis oe | cients why
Dimensions and aspect of og 3 5 6 o 2 | s oS Bae Remarigs
planes. Sa) = | S82 | see| e8
2 |2 |e2s|e22| 5
a ie Pe -
|
15 19 eal Soret 7Or te sa) oss
| Been. G ie20 5.4 | 0.69
aa oe BSE |e 465 ie 127-2, 2'80
15x4 inches (881x102]/ A |— 7| 4.90 12.6 0.58
em.). oe = it a fu al) 5A | 0.58
Double pair of planes, 4 A {+10} 8.60 1.2 0.80
inches apart. A ;+10 4.70 WB: loses Soars.
Total weight, 942 grammes. 3 |+10] 11.00 5.6 | 0.60
Same planes, 2inchesapart.| A 0°) 11.40 iy 0.58
ys a 0} 11.00 5.6 0.56
A 0| 4.90 12.6 | 0.69
B 0 4.50 12.8 0.68
AL le 5 |, 4°50 Ball 1.13
eae a O30 6.0 0.60 |
BW 9.20 6.7 | 0.55
sh 4.80 12.8 | 0.55
SP 4.90 12.6 | 0.74
ot 9.70 6.4 | 0.60
= 9.90 6.2 | 0.56

Single pair of planes, 15 x 4
inches (38.1 x 10.2 em.).

eoleslecloept-ae—leelles|l=

Perr OWerre

rrr rrr ram

4.95 12.4 0.60
4.95 12.4 1.50

ares |

5
5
5)
5)
5
5
a
ta AOO 5.6 0.50
7 | 10.60 5.8 0.52
— 7| 4.80 12.8 0.50
+ 7 4.60 13:4 1.30
+ 7 9.10 6.8 0.60
— 7 8.75 7.0 0.54
— 7 4.90 12.6 0.58
+ 10 4.80 12.8 3.45
+10) 10.60 5.8 0.60
+10} 10.20 6.0 | 0.61
+10] 4.90 LOG len}
+11 4.90) 12.6 | 11.30 | Falls slowly.
+12 4.90 12.6 | 27.50 | Falls very slowly.
+14) 4.95 12.4 | 27.65 | Falls very slowly.
+14) 4.70 Ll ee ee es Soars.

0°) 460 | 134 | 090 |

0 4.60 13.4 0.99
0} 845 7.3 | 0.64
0} 8.40 7.3 | 0.65
+ 5) 845 Ue |) OS) |
+ 5 5.00 12.5 1.37
+ 7 5.00 117733 2.50 |
+ 7} 840 (es) I] (OMS) |
+10} 7.90 ish || bes) [soar.
}+10) 5.00 12.3 |11.20 | Falls slowly, but does not

44 EXPERIMENTS IN AERODYNAMICS.

Tapte XI.—Aveusr 24, 1889.

Barometer, 734.3 mm.; mean temperature, 25°.0 C.; wind, light.

|S 2 Sieh: | re) ee Z
Remeice ests) eee |e
: re ea @ d|s65|a2 |e
paaes Fney aspect of | c2 o= & is Z 2 2 zg a g Remarks:
| 5 7 aS ons iS = S ) a
B BOE cS Sa ieee a alee
Remiece | B
Single pair of planes, 15x4 | A |— 5° 9.50 6.5 0.60,
inches. B /+ 5 9.50 6.5 0.65
B |+ 5 5.00 13} 1.30
qs 1s A |— 5 4.95 12.4 0.60
ae Saal A |—7| 485 | 127 | 050
15 15 A |— 7 8.65 Toll 0.60
1) Nap 0 9.40 6.6 | 0.70
B |+10 8.75 7.0 0.70 |
B |+10 4.95 12.4 1.85
B |+12 5.00 12.3 2.70
B |+14 5.10 PAL 1.60
B |+14 4.50 13.7
A 0 2.63 23.4 2.60
18h | 0 2.64 Deis 1.07
A 0 2.60 23.7 1.80 |
B 0 2.60 BAT 1.00
TRO SS at 2.60 SETS ion es | Fell after soaring about 20
B |— 1 2.65 23.3 1.00 | seconds.
3 st i || Deo 23.7 | 4.80 |
A |— 1 2.58 ey) 1.10 |
A |— 5] 260 | 237 | 0.70 |
3 |— 5 2.60 Zou 0.60 |

The actual velocities obtaining in the individual observations varied some-
what; for the lowest velocity ranging between 5 and 8; for the second velocity
ranging between 12.5 and 13.5, and for the highest velocity ranging in gen-
eral between 22.5 and 24.0, except for the planes 6 inches apart, for which the
velocities were about 19 meters per second. The numerical results for the
lowest and the highest speed will be found plotted in Figs. 6 and 7, respectively.
In these diagrams the abscissze are angles of inclination of the planes to the
horizon, and the ordinates are times of falling. For the highest velocity, the
times of falling of the single pair of planes and of the double pair, both, 4 inches
and 6 inches apart, are alike, while for the planes 2 inches apart, the time of falling
is shorter. For the lowest velocity, viz., 6.5 meters per second, the planes 4 inches
apart as well as those 2 inches apart fall a little faster than the single plane,
and are therefore not quite so well sustained by the air.

This result confirms the statement above made, that for double sets of planes,
one above the other, the maximum supporting effect relatively to the single

THE PLANE-DROPPER. ADS

planes is obtained only above a certain minimum velocity of translation. For
the present planes, of size 15 x 4 inches set 4 inches apart, this minimum velocity
is shown by the curves to be higher than 6.5 and less than 23.5 meters per
second, and, from comparison of all the data, apparently lies at about 13 meters
per second. These results substantially confirm those obtained from the experi-
ments of June 14, with this additional information as to the minimum velocity
at which the maximum sustaining power can be obtained for a distance apart
of 4 inches. For a distance of 2 inches apart even the highest velocities show a
serious diminution of efficiency.

The results of these observations with two sets of planes, one above the
other, give us a first conception of the form and initial vertical amplitude of the
wave that is set in motion in the air by a plane passing horizontally through it
in the manner of these planes.

1.25

1,00

0.75

Times of falling 4 feet of single and double pairs of 15 x 4 inch planes set at different angles of
elevation and haying a horizontal velocity of 6.5 meters per second.

Abscissee : = Angles of inclination of plane to horizon.
Ordinates : = Time of fall in seconds.

These later observations also incidentally furnish additional data as to the
velocity of soaring. When inclined at an angle of 10° the single planes and
the double planes, at a distance of 4 inches apart and upward, are sustained in
the air if they have a horizontal velocity of about 13.2 meters per second.
When set at 1°, soaring took place at velocities from 21 to 23 meters per second.
Close observation also indicated that the error of verticality of the plane-dropper
during motion did not exceed 1°; hence for these velocities the soaring angle
may be taken at about 2°. This is a fraction of a degree less than that given by
the observations of June 14, as plotted on Fig. 3.

‘The most general and perhaps the most important conclusion to be drawn from
them appears to be that the air is sensibly disturbed under the advancing plane

46 EXPERIMENTS IN AERODYNAMICS.

See

Times of falling 4 feet of single and double pairs of 15 x 4 inch planes set at different angles of
elevation and haying a horizontal velocity of 23.5 meters per second.

Abscissee : = Angles of inclination («) of plane to horizon.

Ordinates : = Time of fall in seconds.

THE PLANE-DROPPER. 47

for only a very slight depth ; so that for the planes 4 inches apart, at the average
speeds, the stratum of air disturbed during its passage over it, is, at any rate, less
than 4 inches thick. In other words, the plane is sustained by the compression
and elasticity of an air layer not deeper than this, which we may treat, for all our
present purposes, as resting on a solid support less than four inches below the
plane. (The reader is again reminded that this sustenance is also partly due to
the action of the air above the plane.)

Summing up the results obtained with the plane-dropper, we have determined:

1. The relative times of falling a distance of 4 feet (1".22) that obtain for
differently shaped but horizontally disposed planes moving with different hori-
zontal velocities, showing quantitatively the primary fact that the time of fall is
an increasing function of the velocity of lateral movement.

2. The varying velocities of translation at which planes of given size and
weight, but of different shapes, will be sustained by the air when inclined at
different angles.

3. The maximum proximity at which successive planes can be set one above
the other in order to give a supporting power proportional to their surface.

4, A first approximation to the initial amplitude of the wave motion origi-
nated by a plane passing horizontally or at a small angle through the air with a
considerable velocity.

5. The approximate resistance to advance of a wind-plane at soaring speeds,
and (by computation) the work necessary to be expended in overcoming this
resistance,

These experimentally show that the higher horizontal speeds are maintained
with less expenditure of power than lower ones, and the quantitative experiments
by which these results are established are, so far as I am aware, new, and I
believe have a most immediate bearing on the solution of the problem of artificial
flight.

TI may add that these experiments with the horizontal plane, when properly
executed, give results of a character to forcibly impress the spectator ; for, since
there is no inclination, there is no visible component of pressure to prolong the
fall, yet the plane nevertheless visibly behaves as if nearly deprived of its weight.
The pair of 18 x 4 inch planes, for instance, 75 of an inch thick and weighing
464 grammes, has a specific gravity of about 1,660 times that of air; vet while the
retardation due to the still air in the direct fall is but 20°.03, that due to the same
air in strictly lateral motion is 1°.50—a most noteworthy result in its bearing on
the use in mechanical flight that may be derived from a property of the air much
utilized by nature, but hitherto almost wholly neglected in this connection by

man—its inertia.

CHAPTER VI.

THE COMPONENT PRESSURE RECORDER.

The experiments with the Plane-Dropper in the preceding chapter give the
soaring speeds of wind-planes of different shapes set at varying angles, and enable
us by the use of a fundamental formula of mechanics to make a provisional com-
putation of the work expended per minute in their uniform horizontal flight,
neglecting frictional resistances.

Among several conclusions, one of prime importance, namely, that in such
aerial motion of heavy inclined planes the higher speeds are maintained with less
expenditure of power than the lower ones, presents an appearance so paradoxical
that, in view of its obviously extraordinary importance, I have endeavored to
establish it independently wholly by experiment, without the use of any formula
whatever. For this purpose it is desirable to measure by means of a suitable
dynamometer the number of foot-pounds of work done in overcoming the resist-
ance to advance when a wind-plane is driven at soaring speeds (i. e., speeds at
which it maintains a horizontal course by virtue of the vertical component of
pressure, which in this case is just equal to the weight), by means of the whirling
table, yet under conditions strictly assimilable to those of free flight, in the case
of an actual aerodrome propelled by its own motor.

After much study and much experiment, I gradually perfected an instru-
ment (that described here as the Component Pressure Recorder), to be used in
connection With the Dynamometer-Chronograph in recording the speed, the resist-
ance to forward motion at the instant of soaring, and other attendant phenomena.
Its use in connection with the Dynamometer-Chronograph will also be further
described in chapter VII.

In the present chapter, I shall not consider further the action of the self-
propelling model, but treat of it as reduced to its simplest type of an inclined
plane, the “ wind-plane,” or system of planes driven forward by the turn-table
arm until they are raised from it by the wind of rotation and soar. The imme-
diate objects of experiment are, therefore, to determine soaring speeds and the
horizontal resistances corresponding thereto.

DESCRIPTION.

The Component Pressure Recorder (or Component Recorder), plate VII, may
be compared to a balance which rocks on a knife-edge bearing, in the ordinary
way, but which also oscillates horizontally about a vertical axis. With respect

(48)

THE COMPONENT PRESSURE RECORDER. AD

to its vertical oscillations about the knife-edve bearing, it is a true balance, whose
arms, each one meter long, are in delicate equilibrium, and I will call this part
of the instrument distinctively “ the balance.”

Tf an actual working aerodrome model with its motor be not used upon
the outer arm (outer, that is, as reckoned from the center of the turn-table), a
plane of given weight (the “ wind-plane”’) is clamped there, so as to make any
desired angle of inclination with the horizon. The horizontal oscillation about
the vertical axis provides for the measurement of the horizontal component of
pressure on this plane; the vertical oscillation on the knife-edge provides for
measuring the vertical component. The horizontal pressure is measured by the
extension of a spring fastened to an arm moving around the axis with the
horizontal oscillation of the balance, and to the surrounding fixed frame. The
vertical component of pressure is measured only when it is equal to the weight
of the plane—z. e., by the fact that the plane is actually just lifted by the wind
of rotation, or, in the technical term previously used, when it soars. The requisite
registration of this fact is automatically accomplished by making an electric
contact. As the wind-plane is raised, the inner end of the balance descends, until
it strikes a stop through which electric connection is established, and the
“making” of the current is registered on the stationary chronograph, which
at the same time records the speed of the whirling table four times in each
revolution, and thus the horizontal velocity which produces a vertical pressure
sufficient to lift or sustain the wind-plane is determined.

The detailed manner in which these objects are attained by the apparatus
is described later in the text, and is-:shown by the drawings of plate VII. The
letters S designate the iron supports by means of which the frame of the recorder
rests upon the arm of the whirling table in such a manner that the instrument
is half above and half below it. The knife-edge and the wind-plane are brought
thereby into the plane of rotation, and equal surfaces above and below the
supporting arm of the whirling table are exposed to the wind pressure.

The details of the knife-edge bearings are shown on the plate in enlarged
seale. It is evident that when the balance resting on its knife-edge is in motion
on the whirling table, there will be an outward thrust on the instrument tending
to throw the knife-edge off from its bearing. In order to take up this thrust,
and yet in no way impair the action of that portion of the instrument which
acts the part of a balance, a pair of cylindrical pivots exactly concentric with the
prolongation of the knife-edge are made to extend out beyond the knife-blade
and rest in a suitable bearing. The pivots thus arranged take up the outward
thrust arising from centrifugal force, while the freedom of motion of the balance
on the knife-edge is not at all impaired.

y
‘

50 EXPERIMENTS IN AERODYNAMICS.

The wind-plane is fastened to a brass tube on the outer end of the instrument,
and set to any angle of inclination by means of the graduated circle G. This
tube is adjustable in position so that the center of the wind-plane, whatever be
its size, is at a constant distance of 1.25 meters from the center of the balance
and of the whole instrument. A similar adjustable tube on the inner arm
serves to adjust the balance to equipoise for any position of the outer tube.
Beneath the inner arm of the balance a registering arm is rigidly fastened to
the vertical axis, and partakes of the horizontal oscillation of the balance, but
not of its vertical motion. Near its extremity is attached the horizontal spring
already referred to, and at the end it carries a pencil, which registers on a
revolving chronograph cylinder below the extension of the spring produced by
the horizontal pressure on the wind-plane.

The length of the record arm from center of balance to spring is 28.5 inches,
(72.4 em.)

The length of the record arm from center of balance to pencil is 31.5 inches,
(80.0 cm.)

The pencil departures are therefore longer than the true spring extension,
and the latter are obtained from the former by multiplying by the factor

28.5 , is
Se = (LCS.
3)

aD)

To reduce the pull on the spring to what it would be if the spring had the
same lever arm as the center of the plane, we must multiply it by the factor
expressing the ratio of the lengths of the arms, viz., = = 0.579.

Within the limits of attainable precision, we observe the spring calibration
to be linear, and the two factors may be multiplied together, giving the single
factor 0.524, by which the pressure corresponding to pencil departures, as taken
from the calibration curves, must be multiplied in order to get the pressures on
the plane. The horizontal springs used in these experiments are those hereafter
more fully described in connection with the Rolling Carriage.

The uniform distance from the center of rotation of the turn-table to the
center of wind plane is 9.55 meters. The balance arms are protected from wind
by covering the sides of the surrounding frame with cloth and paper and placing
over the top an adjustable lid of veneer. An experimental test of the Recorder
without wind-plane was first made, to discover the effect of any residual wind
pressure on the arms. The instrument was carefully adjusted on the turn-table,
and then set in rapid, uniform motion without exhibiting any tension of the
horizontal spring. The result indicates that whatever wind pressure still
remains is equal on both arms. It is to be noted that a theoretically perfect
measurement of horizontal wind pressure by this instrument requires a uniform

THE COMPONENT PRESSURE RECORDER. 51

velocity of the turn-table at the instant for which the reading is made. The
oecasion for this condition arises in the circumstance that with a varying
velocity the inertia of the inner arm of the balance produces a different effect on
the instrument from the inertia of the outer arm; thus with increasing velocities
the outer arm tends to go slower than the inner arm, and with decreasing veloci-
ties tends to go faster. This differential effect of inertia is taken up by the spring
and is combined with the wind pressure until a uniform velocity is attained, and
then the wind pressure alone remains to extend the spring.

Each arm of the balance carries a brass friction wheel, R, which is intended
to rest upon a track, P P’, thereby limiting the vertical motion of the balance
arms. When the wind-plane is vertical, and horizontal wind pressure is being
measured, the outer arm carrying the plane rests continuously on the track and
the friction wheel affords perfect freedom of horizontal motion of the balance,
which fulfills its proper function at the same time that it turns about the vertical
axis; so that when the plane is inclined and is raised by the vertical component
of the wind—i. e., when the wind-plane soars—the inner arm is brought down
to the stop P and the friction wheel insures free motion of the balance about the
vertical axis. An electric wire connects with P, and a second wire earries a
current through the knife-edges into the balance, and thence to the friction wheel,
where the electric current is completed at the moment of contact between the
friction wheel and the stop. After leaving the whirling table the current passes
through an electric bell, which serves to inform the experimenter of the fact of
soaring (though this is independently recognizable by the motion of the arm),
and thence to the observatory chronograph, where the contacts are registered.
On this chronograph, then, are registered (1) the second-beats of the mean time
standard clock of the observatory; (2) the contacts, which are made four times
in every revolution of the turn-table and show its speed, and (3) the electric
current which registers soaring; the two latter records being clearly distin-
guishable.

The actual method of experiment employed to determine the velocity at
which soaring is just attained is as follows: The velocity of the whirling table
is increased to the point at which soaring almost begins to take place—that is,
when the plane begins to flutter. This velocity is then still further, but very
slowly, increased and adjusted until the electric bell rings as nearly as possible
half the time. The velocity at which this occurs represents that of soaring.
This method is based on the following considerations: If the precise velocity be
attained at which the plane would be just sustained in quiet air, not resting on
the stop at either end, the actual wind which prevails to a greater or less extent
in the open air disturbs this equilibrium and causes the plane to be more than
sustained during the half revolution of the turn-table which carries it against

52 EXPERIMENTS IN AERODYNAMICS,

the wind, and less than sustained during the remaining half. Consequently,
this condition of electric contact half the time is taken to be the one desired, and
the velocity corresponding to it is taken from the chronograph and called the
soaring velocity for the plane and angle obtaining in the experiment. When
the electric bell indicates to the observer an exact soaring, the speed is main-
tained uniformly for a few revolutions, as required by the theory of the Recorder
already alluded to, as a requisite for the proper measurement of the wind pressure
on the plane. A brush H is attached to the inner arm of the balance for the
purpose of producing a regulated friction, and thereby diminishing somewhat
the fluctuations of the apparatus, which was found to be too sensitive to currents
to do work of all the accuracy it is capable of, except in calm weather.

Some preliminary experiments were made in August, 1889, to determine the
relative velocities of soaring of different planes. But the first Component- Recorder
was shortly afterwards destroyed in an accident, and the observations were inter-
rupted until September, 1890, when they were resumed with the newly constructed
and improved Component-Recorder figured in the plate. Nine new planes were
made of light pine, and backed with lead so as to have the following sizes and
weights :

Size. Weight. | Size. Weight. Size. Weight.
Inches. Cm. Grammes. | Inches. Cm. Grammes. | Inches. Cm. Grammes.
30 x 4.8 | 76.2 x 12.2 250, 24x6 |61.0 x 15.2 250, 12 x 12 |30.5 x 30.5] 250,
00 x 4.8 | 76.2 x 12.2 500 24x6 |61.0x 15.2 500 | 12x12 |30.5 x 30.5 500
30 x 4.8 | 76.2 x 12.2 1,000 || 24x6 |61.0x 15.2 1,000 |) 12x12 |80.5 x 30.5| 1,000

It was found that the heavier planes, and especially the longer ones, required
light trussing in order to prevent them from bending when in rapid motion.
This was effected by inserting a transverse arm of round brass in the end of the
brass tube where the planes are attached, and carrying fine steel wire out to the
extremity of the plane. The 30-inch plane was further trussed by a post at its
center carrying wires to the four corners.

Inasmuch as the center of pressure on an inclined plane is in front of the
center of figure (as will be shown in connection with the Cownterpoised Eccentric
Plane), the lead backing was inserted to one side of the center, so as to bring the
center of gravity into approximate coincidence with the center of pressure when
the plane is inclined at low angles, and the plane was grasped at a similar
distance in front of the center. These provisions contributed to diminish the

twisting of the planes. These planes were used until November 25, when they

me

THE COMPONENT PRESSURE RECORDER. 53

were replaced by others backed with strips of brass, which gave the planes the
desired weight, and also contributed the necessary stiffness. The latter planes
are made of pine + of an inch thick, with square-cut edges. The brass strip
is a piece of hard-rolled brass running the whole length of the plane, and about
2 inches wide. In the 24 and 30 inch planes the middle of the strips was bent
slightly outward—. e., ‘corrugated ’—for greater stiffness.

The experiments were made in two series. The first series was made on
eight days, from September 29 to October 9, inclusive, and consisted in deter-
mining the soaring speeds and corresponding resistances of the above-described
planes set at angles from 2° to 30°, and the horizontal pressure on the planes
when set at 90°—that is, normal to the line of advance. In all, 95 complete
observations were taken.

The following is an example of the original record made in these observa-
tions, extracted from the note book for October 8 :

Experiments with Component Pressure Recorder to determine horizontal pressures at soaring speeds.
OcroBER 8, 1890.
F. W. Very, Conducting experiments; Joseru Luprwic, Regulating engine.

Barometer, 736.6; temperature, 15° C.; air meter at 10:30 a. m., 1,509,500; air meter at
3:20 p. m., 1,500,400; 30 x 4.8 inch plane; weight, 500 grammes; spring No. 2.

Masia Seconds in one reyo- | E SER ada Extension of spring | Pull of spring
or Sal lution of turn-table. | endl) pales ea (inches).* (grammes).
90° 12.10 4.96 1.40 45
10.05 | 5.97 2.20 472
9.60 | 6.25 | 2.45 526

*The use of an English scale instead of a metric one in measuring the spring extensions introduces a lack
of harmony in the system of units employed that is not to be recommended; but since this is a record of the
original observations, the measurements as actually made are faithfully presented.

sya EXPERIMENTS IN AERODYNAMICS.

apy oe : Estimated soaring | Spring
Angle Seconds in one revo- | ““. eed (meters per | extension Remar!
4 . s ° © oC . >. ens. 7) rKS
= lution of turn-table. z! } P : a oa
| second). (inches).
|
30° 5.5 >
G3) <=
5.5 > +5.65 secs. | 10.6 2.3
5ID< |
DoS
15° £8) >> )
54 >
5.65 right | ~ + | . . .
63 << fo? 10.4 | 0.8 Plane quivers at tip with
eee highest speed.
oo ‘<
5.85 right }
10° 5.0 >
5.4 right
5.85 < 2 aye me
5 5 = 5.30 17.9 0.75 | Plane somewhat bowed.
5.3 <<
5.3 right
Plane stiffened by thin iron plate at both ends and at middle, and experiment
repeated with same setting.
10° A9 S
On —<—
4.75 > 4.95 2. !
(Repeated) | FPS? ee lila te
: il <_ |
NO ce

The extensions of the spring corresponding to the horizontal component of pressure
on the plane, and caused by the movement of the Recorder about the vertical
axis, are taken from the sheet of the recording cylinder carried on the turn-table
arm, as already described and as shown on plate 7. The records of velocities
are found on the stationary chronograph registering the quadrant contacts of
the turn-table, and on the same sheet with the electric contacts made at soaring
speeds. Thus, when the latter sheet has been taken off its chronograph barrel,
the observer has before him a permanent record of the velocity of the turn-table
measured four times in every revolution, and together with it the trace of the
irregular contacts made by the vertical rocking of the balance arm which takes
place at soaring speed. Now, since the criterion of exact soaring is that these
signals shall appear on the trace half the time of each revolution, an inequality
mark is added to the record of the measured velocities, which indicates how
nearly this condition is attained. If the chronograph sheet for any complete
revolution of the turn-table is more than half filled with the signals, the velocity

THE COMPONENT PRESSURE RECORDER. Do

is too great; if less than half filled, the velocity is too small, ete. Two or more
inequality marks are used to indicate a wide difference from the mean condition.
By putting down a series of such readings measured at a number of revolutions
of the turn-table and taking a mean estimate, a very close approximation to the
soaring speed may be made, and the result has the weight of a very considerable
number of single readings.

After completing the experiments of September 29 to October 9 according
to the plan laid out, the observations were reduced, and their discussion served
to show that additional experiments were needed to supplement them. There-
upon a second series was instituted for the purpose of obtaining additional data.
In this series the following five planes were used :

+

Size. Weight.

|
(Inches.) | (Centimeters.) | (Grammes.) |

30x 4.8 hayes oe WY 500
94x 6 61.0 x 15.2 500
i Disxoltyy 30:5 30!0 | 500
Aiex6 30:5 x 15.2 250

6x 6 Dexa er, 125

The principal further objects to be attained were to determine with greater
precision the soaring speeds of the 24x 6 and 30 x 4.8 inch planes at small angles
and the horizontal pressure at those speeds; to determine the soaring speed for
angles of the plane above 30°, so as to get the minimum point in the soaring
speed curve—that is, to determine the angle at which soaring takes place with
minimum velocity; and to ascertain the effect of size of plane on soaring speed
by adding to the planes previously used two of smaller size, viz., 12 x 6 inches
and 6 x 6 inches, having a corresponding diminution of weight. The five planes,
therefore, all have sizes and weights in the proportion of 500 grammes to the
square foot * (or 5,382 grammes to the square meter), and their soaring speeds are
entirely comparable for indicating the relative effect of shape and size. The new
observations were carried out on November 25, 26, December 5 and 11, and com-
prised over 80 individual experiments. The detailed observations of both series
are presented in Tables XIV and XV, placed at the end of this chapter.

The column headed “ description of planes” gives the dimensions and weight
of the planes. The aspect of the plane—i. ¢., its position with respect to the

*The square foot was adopted as a unit in the earliest experiments, and its use has been continued as a
matter of experimental convenience, owing to considerations bearing upon the uniformity of apparatus. Were

these experiments to be recommenced, I should prefer to use C. G.S. (or at least metric) units throughout.

56 EXPERIMENTS IN AERODYNAMICS.

direction of advance—is indicated by the order in which the dimensions are
stated, the first dimension being always the horizontal edge parallel to the
whirling arm. Thus the 24x 6 inch plane is placed with its 24-inch edge hori-
zontal and parallel to the whirling arm, and the 6 x 24 inch plane is the same
plane placed with its 6-inch edge horizontal and parallel to the whirling arm.
This difference of position, then, will be uniformly spoken of as the aspect of the
plane. The column “pull of spring” contains the spring extensions converted
into pressures by means of the calibration curves, and the column “ horizontal
pressure on plane” (7. é., the horizontal component of pressure) is obtained by
multiplying the spring pressure by the factor 0.524, which arises from the unequal
lengths of the arms of the instrument. The next column, headed ‘“ %,,,” gives
for the observations with normal planes the computed value of the coéfficient in
the equation P=,, V*, where V is expressed in meters per second, and P is the
pressure on the plane in grammes per square centimeter. The column “%” gives
the corresponding value of this coefficient in English measures, the velocity being
expressed in feet per second and the pressure in pounds per square foot.

SOARING SPEEDS.

The soaring speeds determined in these two series of experiments are plotted
in Figs. 8 and 9, in which the abscissze are angles of inclination of the planes to
the horizon, and the ordinates are the soaring speeds which correspond to them.
Figure 8 contains the observations made with the planes that weigh 250 and 1,000
grammes to the square foot, and Fig. 9 those made with the planes that weigh
500 grammes to the square foot (5,382 grammes to the square meter). The
experiments with the first two of these classes of planes, plotted in Fig. 8, were
not repeated, and consequently the curves do not possess so high a quantitative
value as obtains in the case of most of the planes weighing 500 grammes to the
square foot, but they serve to present several fundamental relations :

First, they show quantitatively, when taken together with the curves of Fig.
9, the increase of velocity necessary to sustain the heavier planes (per unit area)
over that which will sustain the lighter ones, at the same angle of inclination.

Second, the curves both of the 250 and the 1,000 gramme planes show the
difference due to shape and aspect, the soaring speeds, for small angles of inclina-
tion, being much less for those planes whose extension from front to back is small,
than for those in which this dimension is large, so that, in general, the planes
having this dimension smaller, for small angles of inclination, soar at lower
speeds. This result entirely accords in character with that already obtained with
the Plane- Dropper; and, when freed from aceidental errors, the present data are
of higher quantitative value, because in this apparatus there are no guides, and
the plane has practically perfect freedom.

THE COMPONENT PRESSURE RECORDER. Sif)

| | A etebanenpti toby arannys
( \R4inch dide horizontal.

B.6x24 inch plage, wt L009 grammes,

(Pinch sick horizorial.)

Bicsd:
28

27

Cc SOx. ple weight 490 grammes
JO wich wide horizoniat.)

FXO inch Plane, erglé GO TUTTE
i (24irnch side| hoizontal.)

ciaaee

Kee ae eda!

Velocities of soaring of inclined planes obtained with the Component Pressure Recorder.
Abscissee : = Angles of inclination (2) of plane to horizon.

Ordinates : = Velocities in meters per second.

8

58 EXPERIMENTS IN AERODYNAMICS.

Third, many of the curves show a tendency to reach a minimum point for
an inclination of the planes of about 30°, the highest angle at which these planes
were used. It was, therefore, seen to be desirable to extend the angles of inclina-
tion far enough to include the minimum point of the curve within the range of
observation. This was done in the ease of four of the planes whose results are
plotted in Fig. 9. In examining these curves, it will be seen that the minimum
point falls between 25° and 35°. It should also be noted that the change in the
soaring speed is quite small for settings between 25° and 40°, and that in a
number of individual observations the real character of the curve over this range
was masked by the errors introduced by wind and weather.

Since the planes whose results are plotted in Fig. 9 all have the same
weight per unit area, the difference in their soaring speeds arises solely from their
difference of size, shape, or aspect. The effect of shape and aspect indicated in
Fig. 8 is beautifully exhibited and amply confirmed in the six comparable curves
of Fig. 9. For low angles, viz., below 15° or 20°, the curves of soaring speed
for the different planes oceupy the following relative positions from below
upward : 30 x 4.8 inches, 24 x 6 inches, 12 x 6 inches, 6 x 6 and 12 x 12, 6 x 24
inches. It will be observed that the planes placed in the above order are
symmetrically arranged. Remembering that the first written dimension is the
horizontal edge, perpendicular to the line of motion, which may be called the
spread, and that the second written dimension is the inclined edge, or the distance
from front to back, it will be seen that, in the above order, the ratio of the spread
to the extent from front to back is uniformly diminishing. In other words, the
planes whose spread is largest in comparison with their extent from front to back
have the smallest soaring speed, and these planes are therefore to be considered
as being, in shape and aspect, the most favorable for mechanical flight. Thus the
30 x 4.8 inch and the 24 x 6 inch planes are favorable forms and aspects, while
the 12 x 12 inch plane and, to a greater degree, the 6 x 24 inch plane are
unfavorable forms and aspects.

Between 15° and 30°, and in general at about 30°, a reversal takes place,
and for higher angles the curves are all found from below upward in the reverse
order. Thus the 30 x 4.8 inch plane, which for low angles soars at the lowest
speed, for settings above 30° requires the highest speed. This relative efficiency
for low angles was manifested in the experiments with the Plane- Dropper, but
the reversal in the position of the curves for higher angles is a relation which
those observations were not sufficiently extended to present. The interpretation
of this reversal will be developed by a consideration of the general relations
existing between these results and the total normal pressure on the planes, and
will also be found to be connected with corresponding changes in the relative
positions of the center of pressure.

THE COMPONENT PRESSURE RECORDER. 59

Inuves, 8)

Velocities of soaring of inclined planes obtained with the Component Pressure Recorder.
Abscisse : = Angles of inclination (2) of plane to horizon.
Ordinates : = Velocities in meters per second.

60 EXPERIMENTS IN AERODYNAMICS.

The pressure on a plane moving normally in the air is usually represented
by the equation
kA V2 B

P= 75000306 (#— 10°) 760’

where Vis the velocity of the plane; A is its area, B the atmospheric pressure
in millimeters, ¢ the temperature in centigrade degrees, and / a coefficient whose
value for a standard temperature of 10° C. is determined by experiment. If the
pressure per unit area is different for planes of different sizes and shapes, it will
be manifested by differences in the resulting values of &. Then, if & be given
its value for a plane of some fixed size and shape, one or more additional factors
must be inserted in order that the formula shall give the pressure on a plane of
any other size and shape. Experiments show that the variations in & for planes
of different shapes and, within the range of experiment, for planes of different
sizes, are very small.

Proceeding now to the case of inclined planes, and for our present purpose
neglecting the pressure and temperature, we may represent the resultant pressure
Pon an inclined plane moved horizontally in the air at an angle a with the

horizon by the equation

P,= Py F(a) =k AV? Fo),

where F (a) is a function to be determined by experiment. From this equation
also we obtain directly the vertical component of pressure

W=P,cosa=k A V* F(a) cosa
and the horizontal component of pressure

R=P,sina=k A V* F (a) sina.

The point to which I wish now to direct especial attention is that, although shape
and aspect of plane have but slight effect on the pressure on normal planes, they
have a most important influence in determining the pressure on inclined planes.
Consequently, (a) must be determined separately for planes of different size,
shape, and aspect. An empirical curve (Fig. 1) representing F («) for a square
plane has been obtained from the experiments with the Resultant-kecorder.

It is obvious that the above equation for W furnishes the basis for determin-
ing F (a) for variously shaped rectangles from the observations of soaring speed
obtained with the Component-Recorder, together with experiments on normal
planes. The vertical component of pressure at soaring speed is the weight of
the plane, & is the fundamental constant of normal pressure derived from
experiments on the normal plane, and V is the soaring speed for the angle «.

=

THE COMPONENT PRESSURE RECORDER. 61

For the 12x 12 inch square plane, and for the 30x 4.8 inch and the 6 x 24
inch planes, which last two are the planes having the extremes of aspect, F (a)
has been computed from the above equation for JV, and the results are plotted in
Fie. 10. In this computation W is 500 grammes; V is taken from the soaring
speed curves for successive values of a, and the adopted value of &,,, viz., 0.0080,
in metric units, is the mean value given by the normal planes in these experi-
ments. Comparing the resulting curve for the 12-inch square plane with the
eurve derived from the experiments with the Resultant Pressure Recorder, we
find the following values :

TABLE XII.

F(a), or the ratio of the pressure on an inclined plane one foot square
’ Y )
to the pressure on the same normal plane.

8 nee 2
g Sse a Saas
e) ae Saat so
ae So S230
iss] 23g sg 45
rs 3.4 Eo 8s
a SSE oer &
g at ie ~ 3.8 | Difference.
A ash OS KS
G4 PS oO SBv
° Sy 5 SSS
Se Sof F&F
oO a S & qaoHo
Sp aS AS 92
Ss ea ona s
<q cy i
45 93 o1 + .02
40 89 88 + .01
85 84 84 .00
30 78 78 00
25 0 69 + .02
20 60 57 + .03
15 46 44 + .02
10 30 30 00
5 15 16 — Ol
i

The agreement between these values of F (a) derived from these two entirely
dissimilar methods of observation (dependent also, as it is, on the experimental
value of &,,) bespeaks the essential harmony of the entire system of results. If,
now, the curves of soaring speed have been determined for the 30 x 4.5 inch
and 6 x 24 inch planes with the same degree of accuracy as for the 12-inch square
plane, the computed values of F (a) for these planes has the same precision as
that for the 12-inch square plane.

Looking at the curves, we find that for small angles the resultant normal
pressure is greatest in the 30x 4.8 inch plane and least on the 6 x 24 inch plane;
but for angles above 30° this relation is reversed.

The reversal in the relative positions of the curves of soaring speed at an
angle of inclination of about 30°, for differently shaped planes, is now seen to

62 EXPERIMENTS IN AERODYNAMICS.

Fie. 10.

Sloe

AAA
Lous

0 5 10 1S 20 25 30 35 40 45 50

eee
a
Bek

S22 aN
a ea

Ratio of the resultant normal pressure (P,) on an inclined rectangle to the pressure (P,,) on
a normal rectangle, computed from experiments with the Component Pressure Recorder.

Abscissee: = Angles of inclination (2) of plane to horizon.
W Eales

Ordinates: = F(a) = ele
( e 1) iF A J 2 COS a IP.

(expressed as a percentage).

THE COMPONENT PRESSURE RECORDER. 63

be due to a reversal in the total normal pressure on the planes.* Thus, shape
and aspect of plane, while having but slight influence in modifying the pressure
when the plane itself is normal to the wind, are most important factors when the
plane is inclined. This predominating influence of aspect is, so far as I am
aware, now for the first time clearly set forth with quantitative data.+

HORIZONTAL PRESSURES.

With every observation of soaring speed, the horizontal pressure on the
plane has been measured by means of a horizontal spring. The detailed obser-
vations in Tables XIV and XV contain the number of the spring used, the
extension of the spring as measured on the trace in inches, the corresponding
pull of the spring, measured in grammes, as taken from the calibration curves,
and, lastly, the computed pressure on the plane, obtained by multiplying the pull
of the spring by the factor 0.524, which reduces the effect of the actually unequal
arms of the instrument to what it would have been were the arms equal. For
angles of 90° the instrument affords an additional method of determining the
constant of normal pressure, and for all these observations the resulting values
of &, and & have been computed. As previously used, the numerical value of &
relates to velocities expressed in feet per second and pressure in pounds per
square foot, and %,, relates to velocities expressed in meters per second and
pressures expressed in grammes per square centimeter.

The horizontal pressures on the inclined planes diminish with decreasing
angles of elevation, and for angles of 5° and under are less than 100 grammes,
Now, for a pressure less than 100 grammes, or even (except in very favorable
circumstances) under 200 grammes, the various errors to which the observations
are subject become large in comparison with the pressure that is being measured,
and the resulting values exhibit wide ranges. In such cases, therefore, the
measured pressures are regarded as trustworthy only when many times repeated.
On the 30 x 4.8 inch plane, weight 500 grammes, fifteen observations of horizontal
pressure have been obtained at soaring speeds. These values have been plotted
in Fig. 11, and a smooth curve has been drawn to represent them as a whole.
For angles below 10° the curve, however, instead of following the measured
pressure, is directed to the origin, so that the results will show a zero horizontal

pee ei Ss a ee ee ee eS ee

* For a further analogy with a corresponding reversal in the position of the center pressure, see Appendix C.

+ Only after completing these experiments has my attention been called to those of Hutton, who appears to
have been the first to make experiments in this field, in 1787, and who, it is interesting to see, appreciated the
necessity of examining this question of aspect. He tried a plane 8 x 4 inches with both the long edge and the
short edge in the direction of the arms of his whirling machine, but failed to obtain any sensible difference in
his resulting horizontal pressure, probably because the friction of his apparatus swallowed up the small differ-
ences that exist in the horizontal component of the pressure at small angles. If he had measured the total
pressure or the vertical component, he would probably haye discovered a difference in the two cases. I also
find that while my experiments have been in progress, Mr. W. H. Dines has likewise been investigating the
effect of aspect, at Hersham, England, with results similar to my own.

64 EXPERIMENTS IN AERODYNAMICS.

lives, iil.

500

40)

300

a
A
rs
or
ee
cd

200

ie
ih
a
Do
ae
pe
=
ee
ie

100

iG
le
ee
Bs

a

os

~

ae

Horizontal pressure (or resistance to advance) on 80x 4.8 inch plane at soaring speeds
obtained with the Component Pressure Recorder.

Abscissee : = Angles of inclination (4) of plane to horizon.
Ordinates : = Horizontal pressure (/?) in grammes.

© Represents points observed.
x Represents points given by equation, Rk — weight X tangent a.

THE COMPONENT PRESSURE RECORDER 65

pressure for a zero angle of inclination. This, of course, must be the case for a
plane of no thickness, and cannot be true for any planes of finite thickness with
square edges, though it may be and is sensibly so with those whose edges are
rounded to a so-called “fair” form. Now, the actual planes of the experiments
presented a squarely-cut end-surface one-eighth of an inch (38™™.2) thick, and
for low angles of inclination this end-surface is practically normal to the wind.
Both the computed pressures for such an area and the actually measured
pressures, when the plane is set at 0, indicate conclusively that a large por-
tion of the pressures measured at the soaring speeds of 2°, 3°, and 5° is end
pressure, and if this be deducted, the remaining pressure agrees well with the
position of the curve. The observed pressures, therefore, when these features
are understood, become quite consistent. The curve represents the result obtained
from these observations for the horizontal pressure on a plane with “ fair”-shaped
edges at soaring speeds.

A comparison of this experimental result can now be made with the formula,
which appears to be nothing else than an expression for a simple resolution of
forces. I say “appears,” since error is so subtle in its intrusion in these cases
that I have preferred to give the matter, even here, experimental confirmation.

From the analysis above given we have the equation R = W tan a, W being
the vertical component of pressure which, at the instant of soaring, is the weight
of the plane. Tor the purpose of comparing the points given by this equation
with the curve deduced from the observed pressures, the former are shown by
crosses on the diagram with the curve. The agreement between the two is
remarkably close, and, according to the standpoint from which the subject is
viewed, we may say that the formula is actually identifiable, as it appears to be,
with a simple case of the resolution of forces, or that the accuracy of the har-
wonized experiments is established by their accordance with an unquestioned
law of mechanics.

WORK NECESSARY TO BE EXPENDED IN FLIGHT.

Having now obtained final values for the horizontal pressure, or the resist-
ance to the horizontal advance of inclined planes, and having determined their
soaring speeds at different angles of inclination, the work necessary to be expended
per minute in propelling such planes through the air is given in kilogrammeters
by the expression 60RV, 2 being the horizontal pressure in grammes, and V
the soaring speed expressed in meters per second.

The following table, XIII, contains a computation, for the case of the 30 x 4.8
inch plane weighing 500 grammes, of the work necessary to be expended per
minute, the values of R being taken from the curve of figure 11:

9

66 EXPERIMENTS IN AERODYNAMICS

TABLE XIII.

| 7.2 . ie ed
eins Horizontal Work expended per | W eight wath planes Bs lik 2
Soaring speed pressure ite form that 1 horse-power
Anole wth : <p 60RV. will drive through the
Peet ee air at velocity V.
o
. Meters _ Feet Gramrcs. Kilogram- Foot | Kilo- Bonde:
per second. per second. meters. | pounds. | grammes.
45° Ly | SiN | 500 | 336 2,434 6.8 15
30 106 | 348 275 175 1,268 13.0 29
15 112 |) 136.7 128 | 86 623 26.5 58
10 124 | 407 | 88 | 65 474 | 34.8 77
5 15.2 | 498 | 45 } 41 297 55.5 122
2 20.0 | 65.6 | 20 | 24 174 95.0 209
|
| | |

This table shows that for an inclination of 2° the velocity of flight which
suffices for soaring is 20.0 meters per second, and that the work expended per
minute to support the plane (weighing 500 grammes) is 24 kilogrammeters, or 174
foot-pounds. The last two columns contain the weight with planes of like form
that one horse-power will drive through the air at velocity V. At 2° this is 95
kilogrammes, or 209 pounds. This, strictly speaking, holds good only for a system
of planes whose weight, inclusive of any actual motor or other attached weight, is
500 grammes per square foot of inclined plane surface, and which is made up of
30 x 4.8 inch planes. The experiments with the Plane-Dropper show that in
horizontal flight at attainable speeds, a system of such planes can be made by
placing one above the other at a distance of about 4 inches without any sensible
diminution of relative efficiency. Whether these relations of power, area, weight, .
and speed, experimentally established for small planes, will hold good in the
same ratios for indefinitely large ones, Iam not prepared to say; but from all
the circumstances of experiment, I can entertain no doubt that they do so hold,
far enough to afford entire assurance that we can thus transport (with fuel for a
considerable journey) weights many times greater than that of a man.

The preceding investigation, which results in an expression for the varying
amounts of work done by an elementary aerodrome driven at the various soaring
speeds corresponding to the various angles given, has been derived for the ease in
which the direction of propulsion of the aerostat is horizontal and in which its
plane makes an angle @ with the horizon. In the case of an actual aerodrome,
however, it will very probably be found advantageous to propel it in the line of
its plane at such an angle (in practice a very small angle) that the resultant
forward motion due to this elevation and to the simultaneous action of gravity
will be exactly horizontal. If in this case its horizontal velocity be represented
by V, the work done per unit of time will be expressed by the product of the

THE COMPONENT PRESSURE RECORDER. 67

weight multiplied by V tan a, the latter factor being the height H to which the
plane is virtually lifted against gravity.

It will be seen, now, that this expression is the same as that derived for the
former case, V being the horizontal forward velocity, and « the inclination of the
plane to the horizon. In order to prove the perfect identity of significance of
the two expressions it, would, however, remain to show experimentally that the
relation of V to a in this new case is the same as that experimentally derived for
the first case. I have made no experiments with which to determine this relation,
but I may say that, since all the circumstances of the resulting motion seem the
same in the one case as in the other, the relation between V and «@ is presumably
the same, and consequently the amount of work done in the second case is
presumably the same as that done in the first case; it is certainly so nearly so
that whenever @ is small (and it always is so in such economic or horizontal flight),
we may, for all practical purposes, assume an identity of the two cases. It fol-
lows that, in soaring with (horizontal) velocity V, the direction of propulsion can
vary between 0° and a® at will, without sensibly changing the amount of work
that is expended, so long as the plane remains at the angle « with the horizon.

The reader who has followed the description of this instrument will see that
the experiments have consisted in measuring with a dynamometer the actual
resistance to motion experienced by planes when just “soaring” or supporting
themselves under all the circumstances of flight in free air, except that the plane
is restricted from the “ flouncing ” caused by irregular currents, etc., and made
to hold a steady flight.

The most important conclusion may be said to be the confirmation of the
statement that to maintain such planes in horizontal flight at high speeds, less power
is needed than for low ones.

In this connection I may state the fact, surely of extreme interest in its
bearing on the possibility of mechanical flight, that while an engine developing
one horse-power can, as has been shown, transport over 200 pounds at the rate
of 20 meters per second (45 miles an hour), such an engine (é. e., engine and
boiler) can be actually built to weigh less than one-tenth of this amount.

68 EXPERIMENTS IN AERODYNAMICS.

Experiments with the Component Pressure Recorder to measure the horizontal pressure on normal and inclined planes
and to determine their soaring speeds.

TABLE XIV—FIRST SERIES.

F. W. Very, Conducting experiments ; JosepH LupEwic, Regulating engine.

Wate Mean barometer Mean temperature | Mean wind velocity
: (millimeters). (centigrade). (meters per second).
1890.
Stoel noc peaponseoosbeoosooNos 741.0 14° 0.30
October 1 Dep MOE acne raos fa Go 738.6 17 1.20
& DT A tai ete chester: 736.6 18 0.50
& Ber rs eae Censor 735.8 15 0.55
e Deca RIOT ba ac eaelTC 734.5 19 0.60
se Hee cagatiy San OR OTOL ieee 727.7 15 0.60
Shot atta bio aac ne eerie as 736.6 15 0.30
: Oh Aick aeeeteR tice Metre ie Sern rpere 740.1 17 0.50
i oe oP | SP ees
fe} re) bo | “x as ae
= =< | S| a | Bis
s se | Sloe | a8 | 58
Date. Description of planes. | g | Attitudeof plane | 368 |% | 3 |g] aS] km. k.
a 3 o81os/e28
S) fens |) || Gace = || BUS
2 San 2 =| | oS =
Ei aa g a 3S oa
< > palletes | fae | 452)
1890. cm. = cm.
Sept. 29) |! 24x 6 inches’ (61.0'x 15:2) |"30°). es ee 12.0 4/ 1.20} 708] 371
Weight, 500 grammes. ND) | SOATING ele -relel=ts 12.2 4] 0.380] 294] 154
rs 10 re eco 13.6 4} 0.20] 229] 120
cm. cm.
Octal 24 xl im ches) (GIRO sxe 522) mA SOM | eyeeiet eerie tacts 9.6 4 | 2.80 |1,858 | 712 | .0088 | .00158
“ | Weight, 250 grammes. 30 | Soaring......... 7.8 4
; 30 ia he actrees 7.8 2| 1.31 | 294) 154
15 Se San raids 8.3 “1! 0.64 | 164 86
Oct. 2 30 Di ia ra clans 79 “1 1.25 | 284) 149
ie 15 OF eevee 8.0 se
i | 10 ae Rerners ease 8.6 “1 0.50] 134 70
ss 5 ES rec 11.8 “1 045 |) 121 63
5 3 | Not quite soaring} 13.3 SOS meelO 53
3 8) || HOES Soo coe oc 15.4 NOS a MOT, 56
2 COS suchas vaya 17.6 i) (heal |) alal3 59
0 | Not soaring 25.0 “| 0.50 | 1384 7
cm. ecm.
Oct eon| 24 x16 cinchresn (Gil Osxn/512)5| 900 Saree teeeise eer 6.7 4/ 0.88] 567 | 297 |.0071 | .00135
i. | Weight, 1,000 grammes. UW benanososaccoboas 7.2 “1.21 | 708) 3871 | .0077 | .00146
: SON Bence taste cance o 9.8 “| 2.80 |1,3858 | 712 | .0079 | .00151
4 HO) || Sie MbOYES Coronas 15.2 “) 1.60} 867 | 454
15 Oa eels 16.2 “1 0.95 | 594) 311
10 Ste ra gevaeeese 19.4 “1 0.68 | 480} 252
5 | Not soaring......| 25.0 “| 0.50 | 397} 208

THE COMPONENT PRESSURE RECORDER. 69

TasLe X1V—Continued.

s Se ea cr LD
2 | = a 32
& mer be ieee | cena
3 A Pe | Be ee
5 yore sWaierea Renee Mebreps I ak
Date. Description of planes. = | Attitude of plane. SiS | ors ee | ahs | bm k
S Secle |e | | ae
60 OA 5 i= 45 Loma) a)
S ates lh a = og
< > 4) eR Ay Ho
1890. cm. em.

Octo lex 12) inches'(B0!5x 80!) 3 POON Sacer cloister 9.5 4 | 2.70 |1,825 | 694 | .0083 | .00157
aS Weight, 500 grammes. SLOT Go eiconntesn Rete caic 8.3 “! 1.84 | 970] 508 | .0079 | .00150
- | 80 | Soaring........ 9.5 “1 OF75 | 510 | 267
« | 15 Si OF sceafera soleus 12.0 eo) O27 2ale | 142
10 SE Fics atlers ote 15.0 Se Les eel 59 83
a 10 is as ens ads 14.6 PaeO:S05 1970s:

s 5 SUN aencrsy Saeeciszs 20.0 BE CORPO SrtA 92
cm, cm.
# 1x Qanches) (80!5563015)h| G08 seer. seein cscs 6.2 | 2.20 | 471 | 247 | .0069 | 00132
- Weight, 250 grammes. SUM Soames 6.6 S02 | aon 127
a 15 Create Gil {1049 | 130 68
ue 10 SO ea eyegevail 10.6 “ | 0.45 | 120 63
~ 5 CO aes ts = 14.6 Bie OSon | 00 52
Y 3 CO Seti sess 16.7 «| 0.40 113 59
«“ 2 ee ee a. 18:3 a=!" Olsou stan | 876
r O | Not soaring....| 28.1 EO FOSON 199) |e 04
cm. cm.

Oca el 2exal rim chesi(BO0!5ex30!5) 5) 90M Seeeiecrer coe 7.0 4} 1.25 | 726 | 380 | .0084 | .00160
3 Weight, 1,000 grammes. OO in| eerie anerensise 9.4 |] DaARss | aL ORY 647 | .0079 | .00150
* 310) || (Sterna Scop banc 12.8 “1 1.85 | 970] 508
Ps 30 Ug ates oe 12.8 | “| 1.80] 953] 499
15 ance ews eychanntale 17.4 a OS) || Zot | Bes}

Oct. 3 15 Ee ROT 16.7 Dy eelto ass) || 203.
= 10 Seren aegayor te 20.0 “1 1.25 | 285 | 149
5 era Sen 25.5 “| 0.80) 199} 104

cm. cm.

Gin |G se BPE stavelnig's (Ali oe Gil.(0)) | SIO a omenoonacooae 6.2 «| 2.65 | 563 | 295 | .0081 | .00155
x Weight, 250 grammes. S10) |} Stoyeinarers oo boon 7.6 Gl) alestss |) Btls |) aol
15 Cee cametonese seas 11.8 | OREO) |) PalSe|| alates
i 10 Ce ese Me nists 14.1 « | 0.60 | 155 81
¥ 5 Soe eS op stay eucis 21.1 ZN) OBS10) || Pal ay |) alate}

. 3 | Nearly soaring. 25.0 |) aL(00) || eG) 1 118}

cm. cm.
f Gea deonchest @lb:ZexiGleO)) ION | Be occimscreelaletarctek 6.3 “| 2.70% 571) 299%) .0081*).00154*
is Weight, 500 grammes. DOE Ga rosales mete ioe 5A “| 2.08 | 4538 | 287 | .0089 | .00169
a OOM Same rasan ieee ok 4.1 “| 110} 256 | 134 | .0085 | .00161
i 30 | Soaring........ 10.5 «| 2.30 | 492 | 258
i 15 SY ts Ae ta Ke 15.2 SOON 9235) |) 123
a | 10 Hiss Soa 20.7 “| 0:85 | 206) 108
gE 5 SOW Sisters sles 27.3 a Ol65 166 87

cm. cm.
cs (sx PH! rine aves} (UG) se(GIL(0)) || $ID) lls coc on bo ono GmRe 7.3 4} 1.70 | 909 | 476 | .0096 | .00182
5 Weight, 1,000 grammes. OOM Pree tiecea a aes: 5.7 “1 0.95 | 597 | 313 | 0108 | .00197
re 80) || fSenwuntess ooo cpec 14.6 «| 1.80} 953 | 499
: 15 ee gtenateensrel 21.4 « | 0.60) 450) 2386
‘ 10 BE De anh 27.3 “| 0.380 | 294 | 154

*Trace was at limit of admissible extension, and hence the correct results are greater than these values.

70 EXPERIMENTS IN AERODYNAMICS.

Taste XIV—Continued.

Neate a ae eae || Onn ees sot
Date. | Description of planes. | | | Attitude of plane. | sS 5 |% | 22 |. S aS | kn I
= | “ 5 og on oa}
| 3 | Se) eye Fes
| 2 PRS Zt sial [eel [es Ze
=z eee|B|e |= | 88
1890. cm. cm.
Oct. 8 | 6 x 24 inches (15.2 x 61.0) | 15 | Soaring......... 21.8 2
i Weight, 1,000 grammes. | 10 WSS Sabb uae be 28.6 ‘s |
©) | Not soaring ....-. 30.0 “| 040) 118 59
cm. cm.
Ooch} thay arest((TMHM 5 WA) || BIO) |p acoacconnaoansoe 5.0 “|! 140} 317) 166 | .0073 | .00138
Weight, 500 grammes. OO eas eens tetepeei: 6.0 “| 2.20) 471 | 247 | .0075 | .00142
HU ne do odadanoooasns 6.2 “ | 245 | 527) 276 | .0076 | .00145
@hO))|| NSCOR MMUAES 6 Ob oO aos 10.6 « | 2.30 | 492) 258
x 10 | Ce Se, Ae ane,t ilg/s9) SOMO} iS 96
a LON 4 ce CSP or ea 121 | «| 090| 216] 118
a Bi beacodosdoee oases 152 9) 9) 0454) ao ace
= | | 3 | Not soaring..... 21.1 «1 0.50 | 134 70
Sta OF). Sse eee oer 25.007, | O90 1 2tGs) cits
| cm. em. | |
[30x48 imches|(716:2/x12!2))! 90) errr testto = silat 5.8 “|! 2.60 | 554 | 290 | .0091 | .00173
re | Weight, 250 grammes. PSO baer scrcacts acto 43 | “| 1.20.) 277] 145 |.0086 | .00163
- OU) SOamin pallette 8.1 | “| 130) 294) 154
ss | 15 CN Winco eae 8.3 “1 0.50 | 134 70
oy 10 See etetcicystaryers 9.3 “) 0.35 | 100 52
a | 5 ee Pet tera 13.3 a) (eG) | ahs} 59
a 3 Wt Soon ee o.c 17.1 “| 0.55 | 146 76
Non ononapeoue ened 26.1 “) 0.50 | 134 70
| eeceetar s/o) skstacehs eheketars 22:2, SS ZO 2a aS
: (OF etinndiocron coms 27.9 “| 1.50) 38386) 176
cm. cm. | =
Oct.» 9130 s742Siamchesi(7 G2 el 2) N90) ete} 5.8 4/ 0.7 490 | 257 | .0082 | .00157
. | Weight, 1,000 grammes. 90 | efareistvecs sksartecror 8.3 aly 909 | 476.0074 | .00141
2 | 30 | Soaring........- 15.2 1 22 ADTLON) 8
3 | | 15 eis Fictocinte ons Wyo Pa) itt 659 | 3845
2 | 15a aaaccae eee 174 | 2| 23 | 492] 9258
‘ | 10 YJ eaqaceubogs 17.9 4
> | | LOS) el ngs gM cey cea 182 | 2/19 | 416] 218
- | D | Se boop oeac 22.6 ilk 855 | 186

Average of 22 determinations of k,, (at mean temperature, 16° C.) = .00816.

Barometer, 7

Description of planes.

24 x 6 in. (24 in. side
horizontal).
Weight, 500 grammes.

THE COMPONENT PRESSURE RECORDER.

TABLE XV—SECOND SERIES.

NoveMBeER 25, 1890.—F. W. Very, Conductor of experiments.

59,

30 mm.; temperature, 10°.0 C.; wind velocity,

2.4 meters per second.

Si ‘Ss 2 of a | OS
a ae Secale ja
5 Ot ise ee asta ae
3 eu f= eect l/s acetal ete eg ES
oS OV Salesian Taal g | de te
- o So Dn BO Bet |
) * se Ne ieaf & oe =
= | Attitude of plane. | == Sle ge lene lao Remarks.
ra ems os |e a
} Wey Oger ica eerie: |e 8
2 SS hl eS B Ss | Sis
= Sa 2) = eet
=) Cia alee ae Bh ore
< = | ZA | & Viet |
| |
45°) Soaring..... a8 10.9} 4) 210) 907 | 476
=F es % Aa |) eer
50 ee Panes 11.2 | 4 | 2.50 |1,070 | 560
5 Peep Soret 16.9} 4
5 Oe ner 17.2) 31) 0.88 82 | 48
3 | Not quitesoaring | 19.4 |....]...... eSgiaioce oe Adopt 19.6 for soaring speed.
30 | Soaring..... ol OCN Relea O NAO os E26
10 ee tee Retr cidelo 13.38) 4 | 0.21 91 48 | Too small extension of spring

|

to give reliable pressure.

NOVEMBER 26, 1890.—F. W. Very, Conductor of experiments.

Barometer, 736 mm.; temperature, 0°.0 C.; wind velocity, 0.3 meters per second.

|

~ | “9p tt) an oA
= jenaia ee | a2
ae 5 | Atti Si |) Yl eS) a aa
Description of planes. | = Attitude of eats 8] on a Bese ia. ke Remarks.
© planes 4) Se) |o go | te iso
nod on aH =) lon] =
S \SGa! 8 |-as Sh | ue
ae, SS rr caes fa ESV
E: fever ees |) | Sa
2 = l2l8 |e lee
| |
Daexopiney (24 ims side: |) sO8| sas aye ae: | 16.6 SH OO 27 | 14 |
horizontal). el | Somecnnee Hon | 18.3 3 | OAO 82} 43
Weight, 500 grammes.) 3 | Soaring...) 16.2 3| 045) 86 | 45 |
5 | oF 14.4 3] 0.57 | 100) 52 | Whose,
tol OE lei tapas es 3 9.03 4 9.50 |1,068 | 558 | .0074 | .00141
| 1D) kongsis oS505 741 | 41] 1.707 749 | 392 | .0077 | .00146
x v= Sg SO Tae a aS aay aie, RATIO
Same plane (Gin.side | 90 |........... 7.99 | 4] 1.85 | 803 | 421 | .0071 | .00136
horizontal). PESOS ete were teresa: 5.86 | 4} 0.97 | 454 | 288 | .0075 | .00142
| |
6 x 6 inches. Ones ss seran!hs 17.96 | 4| 240 |1,021 | 534 |.0071 | .00136
Weight, 125 crammes.| 90 |........... 16:74 | 41 2:05 | 885 | 464 | 0071 | .00136
oe) 5 z <
| 38 | Soaring 20.1 Bi |} (ous) |) fh 48
| 5 | ts 18.7 3] 0.60; 100} 52
} 10 | oe 15.0 3} 0.73 113) 59)|

~I]
lo

EXPERIMENTS IN AERODYNAMICS.

Taste XV—Continued.

g wa fot [2 rs ms
\s 22 |a|@.|e.|83
[peal S95| EB lae] 28 | ae
Description of planes. | = ae Of yas S | 2S ec om k. Remarks.
s ho) # |. | OS laa
au 25/8 |8-|2/88
| op | OF AGodl si |ees a 7B I=
iS me el ete | ae 5 = is)
< | > 4|e ae mo
BE —— —_—_
12 x 12 inches. OU eee rer 16.7 3 | 0.35 40
Weight, 500 grammes.| 0 |.........--. 17.8 3 | 0.40 44
| 2]) Not soar-| 20.7 | 3] 0.70 57
2) |\eeeane 16.7 3 | 0.55 50
3| Nearly | 20.9 Bi) alot) {als |) G2) ||psosoaileocces Adopt 21.4 m. per sec.
soaring as probable soaring
5 | Soaring...} 20.1 3] 130] 152) 80 speed.
10 sal) IGS) 3] 1.70] 180] 94
20 ss alike Sh dico.au|das son Sobonlbousoalsep oo Spring extended to
20 ¢ iil 4} 0.75 | 340 | 178 limit.
380 e 8.9 4] 1.20} 345 | 285
45 g 10.2 4] 2.31 | 985 | 516
SOi\lscencoege ne 8.23 | 4} 2.20] 989 | 492 00148
(5) 0)) reser 845 | 4 |) 228) 976 | ol .00146
DOM Leseers =, Soccer: 9.15 | 4] 2.70 |1,185 | 595 .00146
SON ce tee sry 8.11 | 4] 2.00] 863 | 452 00141
1P Se() ron, (Maia, rch || (0) |p oe sos0 sor 18.6 3 | 0.55 95 | 50
horizontal). 3 | Scarcely | 18.8 3 || OG |) MO || BS foocdcullgoocos Probablesoaring speed,
Weight, 250 grammes. soaring. 19.2 m. per sec.
5 | Soaring...| 17.5 3| 0.78} 115) 60
10 SCE oe: 13.3 3| 1.00} 131} 69
20 o 10.8 3| 1.75 | 182} 95
20 i 11.0 4! 0.33] 159} 838
30 a 10.5 4] 0.77 | 347 | 182
45 re 10.9 4] 1.14} 522 | 273
(SOs tensa cs ore 7.78 | 4] 0.88] 3899 | 209 | .0074 | .00141
(SONS reactance 9.09 | 4] 1.21 | 549 | 288 | .0075 | .00142
OOWIE ractoctec cr 10.89 | 4 | 1.98] 862 | 452 | .0082 | .00156
GON Reererracretrs.: 12.50 | 4 | 2.55 |1,089 | 571 | .0079 | .00150
OU serves crerctar 11.19} 4 | 2:02 71 | 456 | .0079 | .00149
GON eee 10.00 | 41 1.60| 704 | 369 |.0079 | 00151!
90 scr crap etericroe 8.14} 4} 1.00} 463 | 248 |.0079 | .00150
ee Ssjsvela(GOsroejerteks)| (0) Go ansoocgcd 17.9 33) O3%0) 72 | 38
horizontal). 2} Soaring...} 20.1 3| 0.90] 125) 65
Weight, 500 grammes.) 3 re 17.8 3} 1.04] 134] 70
5 : 15.2 83 |) fale) || alekeh |) 7
10 : 12.6 3 | 1.92)|" 197 | 103
V) O)al aes ee as ae ET 3 | 3.34 | 300 | 157
DO ERGe nee kre 11.6 4} 0.70 | 295 | 155
30 | Soaring 10.8 4} 121 | 550} 288
45 11.2 4) 212) 912') 478
SOE atiiertseicey. 8.3 4 | 2.20 | 985 | 490 | .0075 | .00148
SOW betes. corre 10.26 | 4] 3.80 |1,880 | 723 | .0074 | .00141
SO) acre eae of | 8.00] 4] 2.05 | 885 | 464 |.0078 | .00148

THE COMPONENT PRESSURE RECORDER.

Taste XV—Continued.

DecemBer 5, 1890.—F. W. Very, Conductor of experiments.

Barometer, 732 mm.; temperature, -- 1°.0 C.;

wind velocity, light.

: G4 50 es oe
S| 38 he eee
5 SS | | |a jae
“| paiteien laste aa RAI SS
= SE RSHES) rare | ahaa
= | ; ee eal cease al | Cn a
Description of plane. | 3 | Attitude of plane. |= O13 | oS la sla | Remarks.
aS; ea Obl ies Oe |hOrs: Sq
° = a A eS) SR H ee
Sat QoS a0| 0c
Ou Oo 8 8 2 g Na SI
mt | om Sg 5) =) 7 igs tS
oN | Soci; & = aa
a | oO S| i = |S & |
< = A|A i =
| |
12 x 12 inches. 10°, More than soaring.) 15.8 a
Weight, 500 grammes. | 10 | Soaring eomeen aR 15.0 | 3) 1.80 | 191 | 100 |
|
| |
Flange of cone-pulley broke and stopped observations for the day.
Drcemper 6, 1890.
Barometer, 730 mm.; temperature, + 2°.5 C.; wind velocity, calm.
=a HS ob | i al
3 | He ./ 8/6. lealge
eS | aan zl mo — a i Sp
5 | SR eel eral
Description of planes.| 3 Attitude of plane. += 21% | ad leslie Remarks.
irate POD ere eee ICA iret ec
= Sey = L DS e0|} oS
© SaH|2] e IN| Sis
“eh Shei ceiee re zy
eI CS) BE Oe 5 Se
<q > 4 | & ay am
: os
12 x 12 inches. OP) ornate a5 oon cos 12.8 | 8] 2.60 | 245 | 128 | Velocity of soaring not so well
Weight, 500 grammes. | determined as on Noyem-
| ber 26.
20 ee Ehret iL QIG || RA eects elisveutere|| ene atc Velocity of soaring not so well
| | determined as on Noyem-
30 BF nites 10.3 | 4] 1.10 | 500 | 262 ber 26.
45 | oie ene Ceara 11.4 | 4] 2.20 | 939 | 492 | Velocity of soaring not so ac-
45 | Not soaring......| 10.0] 4] 1.82 | 794 | 416 curately determined as on
30 | SES hee 10.0 | 4] 0.85 | 408 | 214 November 26.
BO WNan ie et crate 10.0 | 4] 0.75 | 340 | 178
20 | ys LUE TE 6G be iKOM0) \) 3. |) aloo) |) als} 69
30 x 4.8 inches. Oy PNOtiquite;soanim cele 1ARSm lier |e crete | siete tell tree 14.9 meters per second assumed
Weight, 500 grammes. as soaring speed.

Fine mist throughout the observations.

10

EXPERIMENTS IN AERODYNAMICS.

TABLE

DerceMBer 11, 1890.—F

Barometer, 724 mm.; temperature,

XV—Continued.

. W. Very, Conductor of experiments.

?

; wind velocity, 0.8 meters per second.

3 Rts) alptize |) eee eae ies
5 : So) Blea] ag | ee
Description of planes. a Attitude of as & 1s Be ne 5 =| km. es Remarks.
& plane. 9 5) 2 | as A 1 So
S So Oi] ey Pes Coseile ise
= Sie] "|| Ee || Se am |os
o Os x (=| a, Si
“eb igen ltarsh || ae = Be
q leat a} aes 4 = os
< = Pah ie
iret ising (Gam sl) BOloccogscccons 8.30 | 1] 1.80 | 980 | 487 | .0076 | 0.00144
horizontal). QO a scissors 6 9.15 | 1 2.20 |1,098 | 576 | .0074 | 0.00140
Weight, 500 grammes. | 45 | Soaring 11.5 1 | 2.10 | 1,057 | 558
30 OS recoup nncoas 1 | 0.91 | 557 | 292
20 €f 10.9 1) 047 | 350 | 183
15 § ital 3
Oni hoe cetonns 20.7 3 | 0.20 59 | 31
PHSe() trot, (CHE tno Arey! |b asco cco D coc 20.7 3 | 0.20 59 | 31
horizontal). 10 | Soaring....| 18.0
Weight, 500 grammes. |

Mean of 22 determinations of k» (at temperature 0° C.) = 0.0076.

CHAPTER VII.

THE DYNAMOMETER-CHRONOGRAPH.

Having determined by means of the Component-Recorder the resistance that
must be overcome in moving a material plane horizontally through the air at
different speeds, the next step of my investigation has consisted in devising means
for measuring the power that must be put out by a motor in doing this useful
work; for, by any form of aerial propulsion, the useful work that can be derived
from the motor is only a percentage, either large or small, of that which is
expended. It becomes important, therefore, to determine the ratio between the
propelling force obtained, and the amount of power that must be expended in any
given case.

In devising the following apparatus I have confined my attention to aerial
propellers for reasons of present convenience, and not because I think them the
only practicable method of propulsion, although they are undoubtedly a most
important one.

If we consider the actual circumstances of such experiments, where the motor
under investigation is mounted at the extremity of the large turn-table arm and
is in motion, frequently at a rate of over a mile a minute, and that the end of
this slender arm is 30 feet from any solid support where an observer might be
stationed, it will be seen that the need of noting at every moment the action of
apparatus, which under such circumstances is inaccessible, imposes a difficult
mechanical problem. After trying and dismissing other plans, it became evident
that a purely automatic registry must be devised which would do nearly all that
could be supposed to be done in the actually impracticable case of an observer
who should be stationed at the outer end of the whirling arm beside the apparatus,
which we may suppose for illustration to be an aerodrome moved by a propeller.
The registering instrument for the purposes desired must indicate at every
moment both the power expended on the supposed aerodrome to make it sustain
itself in flight, and also the portion of that power which is utilized in end-thrust
on the propeller shaft, driving the model forward at such a rate as to maintain
soaring flight, under the same circumstances as if it were relieved from all
constraint and actually flying free in a horizontal course in the air, For this
purpose a peculiar kind of dynamometer had to be devised, which, after much
labor over mechanical difficulties, finally became completely efficient in the form

(75)

76 EXPERIMENTS IN AERODYNAMICS.

I proceed to describe and which I have called the Dynamometer-Chronograph.
A plan of the instrument is given in plate VIII. Its method of operation in
measuring and registering (1) the power expended in producing rotation and (2)
the useful result obtained in end-thrust is here separately described.

(1) MEASUREMENT OF THE POWER EXPENDED.

The propeller wheel L, which is to be investigated, is fastened to the shaft
SS’, which becomes its axis, and is driven by a belt running from the pulley.

When the pulley is driven from any source of power, the resistance offered
by the air to the rotation of the propeller develops a torsional force on the shaft
SS. This shaft is divided into two portions at the clock-spring in the upper end
of the cylinder D, so that the torsional force set up by the pulley is transmitted
to the rest of the axis and to the propeller through the spring in question. This
torsional force can and does cause the cylinder E, which turns with the propeller
end of the shaft, to be twisted with respect to D, which rotates with the pulley,
until the force is balanced by the winding tension of the clock-spring. The rela-
tive angular motion between the pulley and the shaft S causes a longitudinal
motion of the cylinder E into the cylinder D, by means of a spiral groove cut in
the cylinder D, in a manner which is sufficiently shown in the drawing, so that
there can be no angular movement of the pulley C relative to the shaft and to
the cylinder E, without a corresponding longitudinal motion of the cylinder E
and of the pencil P’, which registers the amount of this longitudinal motion
on the recording cylinder; and it will be observed that there will be no angular
motion and no linear motion, unless work is being done by the pulley ; for, if the
propeller wheel were removed, or if its blades were set with their planes in the
planes of its rotation, however fast the pulley may be driven, there will be no
record. The linear motion of the pen P” is, then, caused by, and is proportional
to, the torsional force exerted by the pulley, and to this only. It is obvious that
if the recording cylinder revolve at a known rate, the pencil trace will give a
complete record of the two necessary and sufficient factors in estimating the total
power put out, namely, the amount of this power from instant to instant (how-
ever it vary) and the time during which it is exerted; the former being given by
the “departure” of the pen from its normal position, the latter by the length of
the trace, so that a complete indicator-diagram showing the power expended is
found on the sheet when it is unrolled from the cylinder. The abscissa of any
point in the developed curve is proportional to the time; its ordinate, which
represents the departure of the pencil parallel to the axis of the cylinder, is pro-
portional to the tension of the clock-spring. The value of this departure, or the
actual stress it represents, after allowing for all circumstances of friction, is
obtained by calibrating the spring by hanging weights on the circumference of

THE DYNAMOMETER-CHRONOGRAPH. AU

the pulley. This departure, then, corresponds to the effect of a definite and
constant weight so applied, so long as we use the same spring under the same
adjustment. When widely different ranges of power are to be measured, the
additional range of tension required is obtained with the same spring by insert-
ing a set-screw in successive holes, numbered 0 to 15, around the end of the
eylinder D, so as virtually to shorten or lengthen the clock-spring. A separate
ealibration is, of course, required for each setting.

(2) MEASUREMENT OF THE END-THRUST.

I have thus far spoken of the shaft or axis as if it were in one piece between
the clock-spring and the pulley, but for the purpose of measuring the end-thrust
the shaft is also cut in two within the cylinder F. The two pieces are maintained
in line by suitable guides, and forced to rotate together by a fork within I’, but
the propeller end of the shaft is given freedom of longitudinal motion. Any end-
thrust on the axis, whether received from the propeller or otherwise, causes, then,
this portion carrying the pencil P to slide up within the other toward the pulley,
telescoping the part of the shaft next the propeller within that next the clock-
spring, and causing the longitudinal compression of the spiral spring in cylinder
F, as shown in the drawing. All the parts of the axis, then, between the
clock-spring and the propeller must rotate together when the latter is revolved,
but the end of the axis nearest the propeller, and this end only, has the
capacity not only of rotatory but of a longitudinal motion, which latter is per-
mitted by this portion of the axis telescoping into the other, as above described.
The force of the end-thrust is recorded by the “departure” of the pencil P, which
bears a definite relation to its own spring, determined by independent calibration.
The record made by P on the recording cylinder is a curve whose abscissie are
proportional to time and whose ordinates are proportional to end-thrust. This
curve cannot by itself properly be called an indicator-diagram, since, taken
alone, it records a static pressure only, but when the experiments are adjusted
in a manner later described in this chapter the record of the speed of the turn-
table (on which it will be remembered this apparatus is being carried forward)
supplies the requisite additional data that an indicator-diagram demands. Hence,
while the pencil P” actually traces an indicator-diagram giving the expenditure
of power at every moment, the pencil P traces in part a second indicator-diagram
giving synchronously the useful result attained.

A third pencil, P’, records the seconds of a mean time-clock through the
action of an electro-magnet, M, and obviously gives the means of determining
with all needful precision the time corresponding to each element of angular
rotation of the cylinder, even should this vary. This time record, then, serves
two purposes: (1) it gives the speed of rotation of the cylinder, and (2) permits

78 EXPERIMENTS IN AERODYNAMICS.

the traces to be synchronized with the speed of the whirling table registered on
the stationary chronograph.

The cylinder is rotated in either of two ways: (first) by the driving pulley,
through a system of gearing, which gives the cylinder rates of rotation equal to
4000) 200; OF qovy that of the driving pulley according as desired, so tnat the speed
of the pulley is thus measured by the rate of rotation of the cylinder; or (second)
the cylinder may be independently rotated by an attached clock when it is desired
to give it a uniform motion rather than to record the speed of the pulleys. In
practice the clock and recording cylinder have been used as the registering appa-
ratus in most of the experiments already described with other instruments.

The drawing shows a portion of an actual dynamometer trace which was
obtained with the instrument when set in motion by a foot-lathe, the power
supplied by the foot through the fly-wheel of the lathe being transferred by a
belt to the pulley and thence to a propeller wheel carried at the end of the shaft
S. The pencil P’, it will be remembered, is connected with the clock-spring, its
“departure,” or motion parallel to the axis, being in this case at every instant
proportional to the tension at the same instant at the circumference of the pulley.
P’ is the pencil, which records every beat of the mean time-clock, while the trace
made by the third pencil, P (in the case actually under consideration, in which
the dynamometer is at rest), measures the static end-thrust obtained from the
propeller blades for the amount of power put out. I may ask attention to the
comparability of these two absolutely independent traces, and invite the reader
to note how perfectly the relation of end-thrust obtained responds to the power
expended. The person turning the lathe did so with the greatest uniformity
attainable by the use of a heavy fly-wheel, but every motion of the foot is, never-
theless, as will be seen, most conspicuously registered. Every change in the
amount of power finds also its counterpart in a variation of end-thrust, and the
inequalities in the application of the power during a single revolution of the fly-
wheel of the lathe may be distinctly traced not only in the first of the two curves
but in the second. (It is interesting to note that in each stroke the power pen P”
starts up sharply and then comes nearly or quite back to the zero line, although
we see from the pen P that work is being done all the time. This is repeated
substantially at every stroke of the foot, in spite of the inertia of the lathe fly-
wheel, and is an indication of the extreme sensitiveness of the apparatus.)

Preliminary to the use of the dynamometer it was necessary, as has been
explained, to calibrate the clock-spring and the end-thrust spring and prepare
curves or tables for evaluating the readings of the traces.

The clock-spring was calibrated in the following manner: The propeller
end of the axle being held fast, weights were applied at the circumference of the
large pulley, 10 centimeters diameter, by means of a cord. The torsional force

THE DYNAMOMETER-CHRONOGRAPH. 79

of these weights at a lever-arm of 5 centimeters (the effective radius of the pulley)
is balanced by the tension of the clock-spring and is measured by the longitudinal
motion of the pencil P’.. On account of the appreciable friction of the guide-
wheel in the helical groove, two measures are desirable for exact calibration in
each case at an upper and lower limit of repose. The mean of these is taken as
the true extension for the given weight, and the observation is repeated three
times with each weight to eliminate errors of observation. This series of observa-
tions was made with the set-screw in the “0” hole, the 5th hole, and the 10th
hole, in order to get a sufficiently wide range of action for the instrument.

The following table, XVI, gives the system of calibration obtained from
experiments made November 14, 1890—F. W. Very, observer :

TABLE XVI.

Calibration of Clock-Spring of Dynamometer.

Weight applied at circumference of large pulley, effective radius 5
centimeters, by cord passing over a small pulley at edge of table.

Weight. | Extension of trace.
Position of set-screw.
Pounds. |Grammes.| Inches. | Centimeters.
LOthwholesaeecescee: 4.32 1,960 1.54 4.67
4.10 1,860 1.70 4.32
3.88 1,760 1.49 3.0
3.44 1,560 1.02 2.59
3.22 1,460 0.86 2.18
3.00 1,860 0.60 1.52
2.78 1,260 0.37 0.94.
film InolWei5 Sada omodone 3.00 1,860 1.82 4.62
2.78 1,260 1.60 4.06
2.56 1,160 iL 33) 3.43
2.34 1,060 IL ls 2.92
Dele, 960 0.88 2.2
1.90 860 0.66 1.68
1.68 760 OAL 1.04
Et () aah olosmieeiee tier 1.83 830 1.86 473
1.61 73 1.64 417
1.30 630 1.39 3.53
ily 530 1.18 3.01
0.95 430 0.91 Dil
0.73 33 0.71 1.79
0.51 230 0.49 1.24
0.29 130 0.25 0.63
0.07 30 O15 0.38

50 EXPERIMENTS IN AERODYNAMICS.

The end-thrust spring was calibrated by suspension of weights in a similar
way. The following calibration was obtained from experiments made March 8,
1888 :

Calibration of End-Thrust Spring.

Weicht. Extension of |

trace. |
| (Grammes). ( Centimeters).
| 100 0.43
200 1.07
300 1.75 |
400 2.21 |

The method of computing the horse-power expended, and the return in end-
thrust obtained, may now be illustrated in the reduction of the following observa-
tions taken without change from the original notes:

OcroBER 380, 1888.

Six-bladed propeller, with blades set at 45° with axis. Dynamometer driven by belt from a
small dynamo. Belt driving 2.1 inch pulley. Dynamometer geared so as to give one revolution
of cylinder for 2,000 revolutions of pulley. Time of one revolution of cylinder, 295 seconds.
Departure of pencil of clock-spring (set-screw in “0” hole), 1.43 inches.

60 x 2000

Driving pulley makes 505

revolutions per minute. Circumference of

2.1 x 3.1416 = : 0 x 2000 x 2.1 x 3.1416
pulley equals eee feet. Velocity of belt equals oO soe i ~ feet

per minute. From calibration of March 8, 1888, an extension or departure of
1.43 inches of the pencil of the clock-spring, with the set-screw in “0” hole,
is equivalent to.a weight of 1.35 pounds on a 3.9-inch pulley. The tension on

. O50 . 3 , . .
the present 2.1-inch driving pulley is therefore 1.35 x = pounds. Multiplying
tension of belt by velocity of belt and dividing by 33,000, we have the work
expended per minute expressed in horse-power, viz:

60x 2000, Tee) ae 1.35 i

CICA R yet se TTY | tS mot
It will be noticed that in this expression the factor 2.1 has dropped out, and the
only variables are the time of one revolution of cylinder and the tension on the
spiral spring taken from the calibration curve. If the former be represented by
a and the latter by b, and the gearing remain unchanged, the horse-power in any

experiment will be given by the formula 3.713 x ‘.

THE DYNAMOMETER-CHRONOGRAPH. 81

I liave now to ask attention to a condition of vital importance in the experi-
ments, and yet one which may, perhaps, not appear obvious. It is, that it is
indispensable that the power expended on, and obtained from, the propeller shall,
for its economical use, be expended on fresh and undisturbed masses of air. To
make my meaning clearer, I will suppose that the Dynamometer-Chronograph is
mounted on a fixed support in the open air, with the axis pointing east and west,
and that in a perfect calm a certain amount of power (let us suppose 2 horse-
power) is put out on a pulley and through it on the propeller, giving a certain
return in end-thrust. Under these circumstances, let the wind blow either from
north to south or from south to north; that is, directly at right angles with the
axle, so that it might at first sight appear that nothing is done to increase or
diminish the amount of end-thrust to be obtained. The amount of end-thrust
under these circumstances will, in fact, be very greatly increased (even though
the constant expenditure of » horse-power be maintained)—so greatly increased,
that a neglect of such considerations would completely vitiate the results of
experiment, the great difference being due to the fact that the propeller-wheel is
now operating from moment to moment on fresh masses of air whose inertia has
been undisturbed.

This being understood, it is not desirable for our purpose to experiment
upon the case where the air is carried at right angles or at any very considerable
angle to the propeller shaft
principle. The circumstances of actual motion cause the wind of advance to be
always nearly in the line of the shaft itself; and this condition is obtained by
moving the instrument so that the wind of advance caused by the motion of the
turn-table is in this direction. It is this supply of fresh material (so to speak)
for the propeller to work upon, which causes the need of noting minutely the
speed of advance, as affecting the result, so that for a given constant quantity of
power expended, the percentage of return in end-thrust depends upon the rate
of supply of fresh and undisturbed masses of air. These considerations very
intimately connect themselves with the theory of the marine screw-propeller, and
the related questions of slip and rate of advance, but I have preferred to approach
them from this somewhat less familiar point of view.

The dynamometer and propeller were therefore mounted, as has been said,
on the end of the whirling-table. The propeller was driven by means of its

a case which is used here only for illustration of a

pulley C by a belt from a small electro-motor also on the turn-table, the motor
being actuated by a current from a stationary dynamo, shown on plate II. This
dynamo sent a current through the brush contact B of the whirling-table to the
small electric motor mounted on the arm. The whirling-table was then raised

11

82 . EXPERIMENTS IN AERODYNAMICS.

out of its gearings by the means shown in plate II, and with full current from
the dynamo the little propeller blades proved capable of rotating the great turn-
table, though slowly, for manifestly the work to be done in moving this great
mass was quite incommensurate with the capacity of a small propeller of 15 or 20
inches radius, Some special means must therefore be devised for utilizing the
advantages given by the attainable speed, steadiness, and size of so large a
whirling-table, without encountering the disadvantages of friction, resistance of
the air to the exposed surface, and similar sources of difficulty. To place the
propeller wheels, either actually driving inclined planes or models, or otherwise,
so far as possible under the conditions they would have in actual free flight, and
to measure the power put out in actuating them, the resistance experienced, etc.,
under these conditions, is evidently an object to be sought, but it is equally
evident that it is difficult of attainment in practice. Much study and much
experiment were given to this part of the problem, with the result of the inven-
tion, or rather the gradual evolution through successive forms, of the auxiliary
instrument described in the last chapter as the Component Pressure Recorder.
This conception of a method by which the Dynamometer could be effectively
used was reached in February, 1889, and, together with its final mechanical
embodiment, was the outcome of much more thought than the invention of the
Dynamometer itself.

As already stated, one of the objects of the Dynamometer is to determine the
power necessary to be expended in mechanical flight ; but manifestly this must be
done indirectly, for we have to experiment with a model or an inclined plane so
small as to be incapable of soaring while supporting the relatively great weight of
the Dynamometer-Chronograph, even if it had an internal source of power capable
of giving independent flight (which the simple inclined plane has not). If such
a working model were placed upon the end of the turn-table arm, with the
Dynamometer supported on this arm behind or beneath it, and if the arm of the
turn-table were without inertia and offered no resistance to the air, the whole
might be driven forward by the reaction of the propeller of the model, actuated
by a motor, until the latter actually soars, and the Dynamometer supported on
such an imaginary arm might note the work done when the soaring takes place.
This conception is, of course, impossible of realization, but it suggests a method
by which the actual massive turn-table can be used so as to accomplish the same
result. Suppose the model with attached propeller and Dynamometer to be placed
on the end of the whirling arm, and the latter rotated by its engine. Further,
suppose the model aerodrome be also independently driven forward by its pro-
peller, actuated by an independent motor, at the same speed as that of the table;
then, if both speeds are gradually increased until actual soaring takes place, it is

THE DYNAMOMETER-CHRONOGRAPH. $3

evident that we reach the desired result of correct dynamometric measures taken
under all the essential circumstances of free flight, for in this case the propeller is
driving the model independently of any help from the turn-table, which latter
serves 1ts purpose in carrying the attached Dynamometer.

As a means of determining when the propeller is driving the model ata
speed just equal to that of the turn-table, let the whole apparatus on the end of
the arm be placed on a car which rolls on a nearly frictionless track at right
angles to the turn-table arm. Then, when the turn-table is in rotation, let the
propeller of the model be driven by its motor with increasing speed until it
begins to move the model forward on the track. At this moment, that is, just
as the acrodrome begins to move forward relatively to the moving turn-table,
it is behaving in every respect with regard to the horizontal resistance (@. ¢.,
the resistance to advance), as if it were entirely free from the table, since it is
not moved by it, but is actually advancing faster than it, and it is subject in this
respect to no disturbing condition except the resistance of the air to the bulk of
the attached Dynamometer. In another respect, however, it is far from being
free from the table, so long as this helps to take part in the vertical resistance
which should be borne wholly by the air; the aerodrome, in other words, will
not be behaving in every respect as if in free air, if it rests with any weight on
the track. The second necessary and sufficient condition is, then, that at the
same moment that the model begins to run forward with the car it should alse
begin to rise from it. This condition can be directly obtained by rotating the
turn-table at the soaring speed (previously determined) corresponding to any
given angle of the inclined plane.

This conception of a method for attaining the manifold objects that I have
outlined was not carried out in the form of the track, which, although constructed,
was soon abandoned on account of the errors introduced by friction, etc., but in
the Component Recorder, whose freedom of motion about the vertical axis provides
the same opportunity for the propeller-driven model to run ahead of the turn-
table as is offered by the track. This instrument, therefore, a part of whose
functions have been described in the preceding chapter, has been used as a neces-
sary auxiliary apparatus to the Dynamometer-Chronograph, and this is an essential
part of the purpose for which it was originally devised. In naming the instru-
ment, however, only a part of its purpose and service could be included, or of
the mechanical difficulties that it surmounts indicated.

The investigation of the velocity at which an inclined plane will sustain its
own weight in the air, and the determination of the end-thrust, or horizontal
resistance, that is experienced at this velocity, were made with the Recorder
independently of the Dynamometer, and have been presented in detail in chapter

84 EXPERIMENTS IN AERODYNAMICS.

VI. The investigation of the power that must be expended to furnish this end-
thrust, and the determination of the best form and size of propeller for the pur-
pose, combines the use of the two instruments.

In the center of the Recorder is provided a place (see plate VII) for the
electric motor already referred to, whose power is transmitted by a belt to the
pulley of the Dynamometer-Chronograph, which is mounted on the end of the rigid
arms. It may be observed that, in this manner of establishing the motor, the
tension of the pulley, however great, in no way interferes with the freedom of
motion of the arms of the Recorder—a very essential mechanical condition, and
one not otherwise easily attainable. With the various pieces of apparatus thus
disposed, and with the propeller to be tested fastened to the shaft of the Dyna-
mometer, the whirling table is rotated at any desired speed. The propeller is then
driven by the motor with increasing amounts of power until the forward motion
of the Recorder arm about its vertical axis indicates that the propeller is driving
the Dynamometer ahead at a velocity just exceeding the velocity of the whirling-
table. ‘This is the moment at which all the records admit of interpretation. The
work that is being done by the propeller is that of overcoming the resistance of
the air to the bulk of the Dynamometer, and in place of this we may substitute,
in thought, the resistance that would be caused by an aerodrome of such a size
as to produce the same effect. The power put out and the resistance to advance
are both registered on the cylinder of the Dynamometer. The result realized is
found by multiplying the static pressure indicated by the pencil which registers
the end-thrust by the velocity of the turn-table at the moment when the pro-
peller’s independently acquired velocity is just about to exceed it. The static
pressure represents the resistance overcome, and the velocity of advance gives
the distance through which it is overcome per unit of time. The product there-
fore represents the effective work done per unit of time. If the adopted velocity
of the whirling-table be the soaring velocity of an aerodrome which would have
the actually observed resistance, the experiment will virtually be made under all
the conditions of actual horizontal flight. In practice, the experiments were
made at a series of velocities, and the results obtained—power expended and
useful work done—can be interpolated for any desired speed.

Preliminary experiments were made with wooden propellers having four,
six, and eight blades set at different angles with the axis. Lastly, two aluminum
propellers were used having only two blades each, extending 24 and 30 inches,
respectively, from tip to tip.

In order that the reader may follow the method of experiment in detail, the
following description of experiments made November 4, 1890, is here given,
together with abstracts from the original record of observations for that date :

THE DYNAMOMETER-CHRONOGRAPH, 85

November 4, 1890.

Continuation of experiments with 30-inch (diameter) two-bladed aluminum propeller to determine ratio
of power put out to return in end-thrust obtained.

Dynamometer-Chronograph with attached propeller is placed on outer arm of the Component-
Recorder and driven by an electric motor placed in the center of the Recorder. The electric motor
is run by a dynamo, the current from which is carried to the heavy brush contact B (plate IT) of
the turn-table, and thence along the arm to the electric motor, and the dynamo itself is run by
the steam-engine which drives the turn-table.

In the manner already described, the pencil P” of the Dynamometer-Chronograph registers the
power put out; P’ registers seconds from the mean time-clock, and P registers the end-thrust of
the propeller. A fourth pencil is fixed to the frame of the Recorder and registers on the dyna-
mometer cylinder the forward motion of the Recorder arm about its vertical axis against the ten-
sion of a horizontal spring, the spring being disposed so as to be extended by the forward motion
of the outer arm. Thus, when the propeller is driven at such a velocity as just to exceed the
velocity of the turn-table, the outer arm bearing the Dynamometer moves forward, the horizontal
spring begins to extend, and its extension is recorded on the Dynamometer sheet, together with the
power put out, the amount of end-thrust obtained, and the time trace from the mean time-clock.

Preliminary to the experiments the surface of the inner arm of the balance was increased so
that the resistance of the Dynamometer on the outer arm to the wind of advance should be largely
counterbalanced. This was accomplished by adding a surface of 17 square inches at a distance
of 4 inches (104 centimeters) from the axis of rotation.

h. om. :
At 2 12 Casella air-meter reads 1,779,600.
At 5 39 ze z ete sole 900!

Toward end of experiments, wind almost entirely died away.

Dynamometer-Chronograph sheet No. 3—notes and measurements :

Propeller blades set at angle of 75° with axis. Horizontal spring No. 3.

Pulley cord of Dynamometer running on 4-inch pulley.

Chronograph cylinder geared so as to make 1 revolution to 2,000 revolutions of propeller.

Set screw of Dynamometer in “0” hole.

Turn-table driven so as to give linear speed of approximately 2,000 feet per minute.

(a) Dynamo = 1,170 revolutions per minute.

(6) Propeller = eee = 1,032 revolutions per minute.

(c) Extension of power pencil P” = 0.65 inches.

(d) Extension of end-thrust pencil P = 0.20 inches (varying).

(e) Horizontal spring: no appreciable extension, except occasional jumps produced by wind.

(f) Speed of turn-table (from sheet of stationary chronograph in office) = 5.41 seconds in one
revolution = 1,865 feet per minute.

The above entries, taken from the original note-book, will be readily under-
stood in connection with the following explanations :

(a) The 1,170 revolutions of dynamo refer to the revolutions of the dynamo-
electric machine, and are read off by means of a Buss-Sombart Tachometer.

86 EXPERIMENTS IN AERODYNAMICS.

(b) 5.52 is the number of inches of the Dynamometer-Chronograph barrel
revolved in a minute, as determined by measuring the time trace. An entire
revolution corresponds to the entire circumference of the barrel, 10.7 inches, and
(with the gearing used in this experiment) to 2,000 revolutions of the Dynamometer
pulley shaft.

Hence
5.52 x 2000

Sa = 1,032
10.7 re

is the number of revolutions of the Dynamometer pulley per minute at the time
of this experiment. The effective diameter of the pulley being 4 inches, this
gives for the velocity of the cerd 1,063 feet per minute.

(c) The extension of the power pencil P” = 0.65 inches. From the calibra-
tion tables we find that this corresponds to a tension of 0.67 pounds on the pulley
cord. The product of this tension by the pulley speed gives the power put out,
viz., 712 foot-pounds per minute.

(d) The extension of the end-thrust trace, 0.20 inch, corresponds to a
pressure of 0 20 pound.

(e) The horizontal spring has no appreciable extension, except as caused by
puffs of wind. This indicates that the propeller is not driving quite fast enough
to equal or exceed the velocity of the turn-table; but the deficiency of velocity is
so small that we shall not discard the experiment, but compute the record as if
the requisite velocity were just attained.

(f) The speed of turn-table multiplied by the end-thrust gives the work
done per minute by propeller, viz., 373 foot-pounds per minute.

We have, then, as a result of the experiment, that the ratio of work done
by the propeller to the power put out is 52 per cent., the form of the propeller
blades not being a very good one.

The whole series of experiments is not given here in detail, but their prin-
cipal results will be communicated in general terms. The first result is that the
maximum efficiency of a propeller in air, as well as in water, is obtained with a
small number of blades. A propeller with two blades gave nearly or quite as
good results as one with a greater number. This is strikingly different from the
form of the most efficient wind-mill, and it may be well to call attention to the
essential difference in the character of the two instruments, and to the fact that
the wind-mill and the movable propeller are not reversible engines, as they might
at first sight seem to be. It is the stationary propeller—i. e., the fan-blower—
which is in reality the reversed wind-mill; and of these two, the most efficient
form for one is essentially the most efficient form for the other. The efficiency
of a fan-blower of given radius is expressed in terms of the quantity of air
delivered in a unit of time for one unit of power put out; that of the wind-mill

THE DYNAMOMETER-CHRONOGRAPH. 87

may be expressed in terms of the amount of work done per unit quantity of air
passing within the radius of the arms. If any air passes within the perimeter
which does not strike the arms and do its work, it is so much loss of an attainable
efficiency. This practical conclusion is confirmed by experience, since modern
American wind-mills, in which practically the entire projection area is covered
with the blades, are well known to be more efficient than the old wind-mills of
four arms.

Turning now to the propeller, it will be seen that the expression for its
efficiency, viz., the ratio of useful work done to power expended, involves quite
different elements. Here the useful work done (in a unit of time) is the product
of the resistance encountered by the distance advanced, which is entirely different
in character from that in the fan-blower, and almost opposite conditions conduce
to efficiency. Instead of aiming to set in motion the greatest amount of air, as
in the case of the fan-blower, the most efficient propeller is that which sets in
motion the least. The difference represents the difference between the screw
working in the fluid without moving it at all, as in a solid nut, and actually
setting it in motion and driving it backward—a difference analogous to that which
in marine practice is technically called “ slip,” and which is a part of the total
loss of efficiency, since the object of the propeller is to drive itself forward and
not to drive the air backward. It may now be seen why the propeller with few
blades is more efficient than one with many. The numerous blades, following
after each other quickly, meet air whose inertia has already yielded to the blades
in advance, and hence that does not offer the same resistance as undisturbed air
or afford the same forward thrust. In the case of the propeller with two blades,
each blade constantly glides upon new strata of air and derives from the inertia
of this fresh air the maximum forward thrust. The reader will observe the
analogy here to the primary illustration of the single rapid skater upon thin ice,
who advances in safety where a line of skaters, one behind the other, would
altogether sink, because he utilizes all the sustaining power to be derived from
the inertia of the ice and leaves only a sinking foothold for his successors. The
analogy is not complete, owing to the actual elasticity of air and for other reasons,
but the principle is thesame. A second observation relating to aerial propellers,
and one nearly related to the first, is that the higher the velocity of advance
attained, the less is the percentage of “slip,” and hence the higher the efficiency
of the propeller. The propeller of maximum efficiency is in theory one that
glides through the air like a screw in an unyielding frictionless bearing, and
obtains a reaction without setting the air in motion at all. Now, a reaction from
the air arising from its inertia increases, in some ratio as yet undetermined, with
the velocity with which it is struck, and if the velocity is high enough it is
rendered probable, by facts not here recorded, that the reaction of this ordinarily

88 EXPERIMENTS IN AERODYNAMICS.

most mobile gas may be practically as great as we please and, with explosive
velocities, for instance, may be as great as would be the reaction of a mass of iron.

The theory of aerial propellers being that for a maximum efficiency, the
higher the velocity, the sharper s should be the pitch of the blades, it has been the
object of the complete series of experiments with the Dynamometer-Chronograph
to determine by actual trial the velocity of advance at which the maximum
efficiency is attained when the blades are set at different angles, and the best
forms and dimensions of the blades. The details of these are reserved for future
publication, but, very generally speaking, it may be said that notwithstanding
the great difference between. the character of the media, one being a light and
very compressible, the other a dense and very incompressible fluid, these observa-
tions have indicated that there is a very considerable analogy between the best
form of aerial and of marine propeller.

CHAPTER VIII.
THE COUNTERPOISED ECCENTRIC PLANE.

If a rectangular plane be made to move through the air at an angle of
inclination with the direction of advance, it was implicitly assumed by Newton
that the center of pressure would coincide with the center of figure. Such, how-
ever, is not the case, the pressure being always greater on the forward portion,
and the center of pressure varying with the angle of inclination.

The object of the present chapter is to present the results of experiments
made to determine the varying positions of the center of pressure for varying
angles of inclination of a plane moved in a horizontal course through the air.
Drawings of the apparatus devised for this purpose are given on plate V. AA’
represents the eccentric wind-plane one foot square held in a brass frame about
& of an inch wide and 2 of an inch thick. Two sliding pieces, SS’, move in a
groove in the edge of the brass frame, and may be clamped in any position by
screws. Each sliding piece has a small central hole, in which fits a pivot, V.
The wind-plane (eccentric plane) is suspended by these pivots and swings about
the axis passing through them, so that by moving the plane in the sliding
pieces this axis of rotation can be moved to any distance up to two inches. A
flat lead weight, which also slides along the back of the plane, can be adjusted
so as to counterpoise it in any position. When the weight is adjusted, therefore,
the plane is in neutral equilibrium about its axis of rotation. A pencil, P, is
fixed on the lower part of the plane and records against a tracing board perpen-
dicular to it. In order to leave the position of the plane entirely uncontrolled
by the friction of the pencil, the registering board is held away from the plane
by spring hinges HH’, and caused to vibrate by an electro-magnet so as to touch
the pencil point many times in a second.

In the experiments the sliding pieces were set so that the axis of rotation
was successively 0 inch, 0.25 inch, 0.75 inch, ete., from the center, and the
plane was counterpoised about this axis. When placed in rotation upon the arm
of the whirling-table, the moment of rotation of the plane about the axis is pro-
portional to the resultant wind pressure multiplied by the distance of the center
of pressure from the axis of rotation, and it will reach its position of equilibrium
when the plane has taken up such an angle of inclination that the center of

12 (89)

90 EXPERIMENTS IN AERODYNAMICS.

pressure is at the axis of rotation. The measurement of this angle is, therefore,
the object of observation.

In actual experiment the exact angle of equilibrium of the plane is masked
by slight inequalities of speed and by fluctuation of the wind, and there is oscil-
lation about a mean position. In measuring the trace, the extreme angles of this
oscillation were read, as well as the mean position of equilibrium.

The following transcript from the note-book for September 22, 1888, will
afford an illustration of the detailed records made in connection with each series
of experiments. The column headed “range” gives the range of oscillation of
the plane, and shows that the plane is far more unsteady when the axis of oscil-
lation and center of pressure is very eccentric than when it is nearer the center.

SEPpreMBER 22, 1888.

Air tempera- | wind direc-

Time. Barometer. ture. aa Air meter.
(Inches.) (Fahr.) on.
10.20 a.m. | 29.080 58.9 N.N.E. 183380
12.20 a.m. 29.069 61.2 INGIN@ EE; 224065

Meteorological conditions not so favorable as yesterday, the wind being rather strong.
Engine run by Eisler; J. Ludewig sets wind-plane; F. W. Very attends to chronograph and records.

Gm (rar sl
ok ong a )
eS nO s = a .
So) eee, = 2
Zaz Ss Sie} SY
. 2S | Sess £5 as
ac 20- oo ==)
Time. 2 8 eel a ee St os Range.
HE! | seS4 os BES
3,2 3 soaks = x
4 A < 3
2 ° o_o
10.88 a.m 12.8 2.00 82.0 64-98 34
10.42 a.m 12.8 1.75 76.0 58-98 40
10.46 a.m 12.8 1.75 76.0
10.50 a.m 12:9 1.50 58.0 48-84 36
12.12 p.m 13.3 0.00 6.0 0.12 12

Two complete sets of observations were made, both on September 21 and
September 22, 1888, making in all 31 separate readings, which are given in detail
at the close of the chapter.

The mean of these observations is presented in the following table XVII:

THE COUNTERPOISED ECCENTRIC PLANE. 91

Taste XVII.

Summary of Experiments giving position of center of pressure on a plane one foot square (30.5 x 30.5

centimeters) for different angles of inclination.

r : :
Distance from center of press- | Distamce as @ | qj oje of trace Angele of plane | Angle of plane
ure to center of plane d. percentage of | 8-4. wey with with
ey with initial Seg pe
the side of the : vertical horizontal
; line. ane
(Inches.) (Centimeters.) plane. 90° — a. a,
a“ 2 2 pote ° _o
0.00 0.00 0.000 5D 0.0 90.0.
0.25 0.64 0.021 17.4 12.0 78.0
0.50 1.27 0,042 28.2 22.7 a
0.75 1.90 0.063 39.7 34.2
1.00 2.54 | 0.083 50.6 45.0
1.25 3.17 0.104 59.7 54.2
1.50 3.81 0.125 67.5 62.0
1.75 4.44 0.146 75.0 69.5

The first two columns give the distance from the center of pressure to the center
of the plane in centimeters and inches, and the third column gives it as a per-
centage of the length of the plane. The fourth column gives the angle of trace
with the initial vertical line drawn through the position of the pencil at rest. It
will be noticed that this angle is 5°.5 for the case when the axis of rotation passes
through the center of the plane—a setting for which the plane must be vertical.
This observed angle of 5°.5 is to be explained, not by a tipping of the plane,
but by a tipping of the line of reference due to a yielding of the supports, etc., to
the wind of rotation. This angular deflection, therefore, becomes a correction to
be applied to all the observations, and the fifth column, headed “angle of plane
with vertical,” contains the corrected values for the inclination of the plane.

The resulting relations here established between the angle of inclination of
the plane and the position of the center of pressure are of importance, but their
application is not made in the present memoir.*

* References to the results of Joéssel and of Kummer will be found in Appendix C.

92 EXPERIMENTS IN AERODYNAMICS.

Experiments to determine the position of the center of pressure on an inclined square plane.
SEPTEMBER 21, 1888.
F. W. Very, Conducting experiments ; JosepH LupEwIG, Assisting.

Barometer, 737.06 mm.; temperature, 18° C.; wind velocity, 0.006 meter per second ; length
of side of wind-plane, 12 inches (80.5 centimeters).

wa q S

a Distance of axis of oscil- S i

BS x lation from center of ane &

oO = od oo
; So plane. 38 as
Time. aera 23 8 Range.

Has 28 a

g S 2 (Inches.) | (Centimeters.) “ep =

A < S
p.m. a ae .
3.17 4.49 1.75 4.44 76.0 65-88 23
3.23 4.49 1.50 3.81 67.5 60-75 15
3.28 4.49 1.25 3.17 60.0 57-63 6
3.33 4.51 1.00 2.54 50.4 47-54 U
3.37 4.47 0.75 1.90 39.0 37-41 4
3.41 4.51 0.50 1.27 29.5 29-30 1
3.45 4.46 0.25 0.64 20.9 19-23 4
3.48 4.49 0,00 0.00 6.4 2-11 $)
3.58 8.47 1.75 4.44 73.0 61-91 30
4.02 8.57 1.50 3.81 67.0 50-80 30
4.06 70 1.25 3.17 60.0 58-63 5
4.09 8.56 1.00 2.54 50.5 47-55 8
4.25 7.92 0.75 1.90 40.1 37-48 6
4.3 8.47 0.50 1.27 28.5 28-31 2
4.41 7.81 0.25 0.64 16.3 15-17 2
44 7.63 0.00 0,00 5.0 4-7 3

THE COUNTERPOISED ECCENTRIC PLANE. 93

SEPTEMBER 22, 1888.
F. W. Very, Conducting experiments; Josep LupEwie, Assisting.
Barometer, 738.4 mm.; temperature, 15.°5 C.; wind velocity, 2.06 meters per second.

Meteorological conditions not so favorable as on the 21st, the wind being rather strong. The
effect is to produce a much wider oscillation of the trace.

~ Distance of axis of oscil- S | %

Be lation from center of = =

os plane. Q'S Sg
Time. PAA 5:8 a) Range.

1 Og oo S +

ako jf Orr 3)

23 (Inches.) |(Centimeters.) "eb B=)

Seate 4 is

|

a. M. Bey Yas: aan
10.88 12.8 2.00 5.08 82.0 | 64-98 3)
10.42 12.8 iL 7A) 4,44 76.0 58-98 40
10.46 12.8 nEvAs) 444 76.0
10.50 1229 1.50 3.81 68.0 48-84 36
10.55 10.4 15) Boll 59.0 385-76 41
11.26 13.6 1.00 2.54 51.0 37-59 22
11.29 13.6 0.75 1.90 40.0 37-43 6
LEY 14.8 0.50 qT 26.5 25-28 3
iil} 13.4 0.25 0.64 15.0 11-19 8
11.41 13.8 0.00 0.00 5.0, 3-7 4
11.58 14.5 2.00 5.08 79.0 58-96 38
p.m.
12.03 14.7 1.50 3.81 66.0 50-80 30
12.06 14.0 1.00 2.54 49.0 45-52 dl
12.09 13.8 0.50 iy 27.0 26-28 2
122 ilaiy38 0.00 0.00 6.0 0-12 12

CHAPTER IX.

THE ROLLING CARRIAGE.

The Rolling Carriage was constructed for the purpose of determining the
pressure of the air on a plane moving normal to its direction of advance.* _What-
ever be the importance of this subject to aerodynamics or engineering, we are
here interested in it only in its direct bearing on the aerodromic problem, and
carry these observations only as far as this special object demands. Before this
instrument was constructed, a few results had already been obtained with the
Resultant Pressure Recorder (chapter IV), but additional observations were desired
with an instrument that would be susceptible of greater precision. The state-
ment has frequently been made that the law that the pressure is proportional to
the square of the velocity fails for low velocities as well as for very high ones.
As it appears to me that this conclusion was probably based on imperfect instru-
mental conditions due to the relatively excessive influence of the friction of the
apparatus at low velocities, particular pains were taken in the present experi-
ments to get as frictionless an action as possible. Plates IX and X contain
drawings in elevation and plan of the apparatus devised for this purpose.

A metal carriage 83 inches long is suspended on a set of delicately con-
structed brass wheels 5 inches in diameter, which roll on planed ways. Friction
wheels bearing against the sides and bottom of the planed ways serve as guides
to keep the carriage on its track. Cushions of rubber at each end break the
force of any end-thrust. Through the center of this carriage passes a hollow
brass rod 273 inches long, on the forward end of which is set the wind-plane by
means of a socket at its center. On the other end is attached a spiral spring,
which is also fastened by a hook to the rear of the carriage-track in a manner
illustrated in the drawing. The rod is of such length that the wind-plane may
be removed from the disturbing influence on the air of the mass of the registering
apparatus, and the center of gravity of wind-plane and rod falls under the center
of gravity of the carriage. The pressure of the wind on the wind-plane is bal-

*These measurements of pressure on the normal plane are not presented as new. They were made as a
necessary part of an experimental investigation which aimed to take nothing on trust, or on authority however
respectable, without verification. They are in one sense supplementary to the others, and although made early
in the course of the investigations presented in this memoir, are here placed last, so as not to interrupt the
presentation of the newer experiments, which are related to each other by a consecutive development.

(94)

THE ROLLING CARRIAGE, 95

anced by the extension of the spiral spring, while the Rolling Carriage bears an
arm, F, carrying a pencil which rests upon a chronograph cylinder to automat-
ically record this pressure, the axis of the cylinder being parallel to the track of
the carriage and the chronograph rotated by clock-work. The position of the
pencil for zero pressure on the spring is marked on the chronograph sheet, and
a reference line is drawn through this point, so that distances of the pencil point
from this reference line are measures of the extension of the spring, while a second
pencil, being placed on the opposite side of the chronograph barrel, and operated
by an electro-magnet in electrical connection with the mean time clock, registers
seconds on the chronograph barrel, and thereby every point of the pressure trace
made by the first pencil can be identified with the synchronous points in the
trace on the stationary chronograph on which is registered the velocity of the
whirling-table.

Much care was bestowed upon the manufacture and calibration of the spiral
springs. The following is a list of the springs, giving their size, length, and
weight :

8 | _~
i = mn
ES a 5 Orem
oO mM =I
[aa = S Se |
VS rs} OR 2
Dice | | q
: B=\ Fon Re) HS aD
B| ‘Ss es = £5 =
ce a= Sal el 3S SRS os
S| oO op 5p = &0
| a 2 Ss = a=
5 3 < =) A aS &
Z = al 4 a =
1 | Steel .. 52 4.5 0.75 64
2 | Brass. . 60 5.0 0.30 18
3 | Steel .. 56 5.6 0.60 43
4! Steel .. 51 5.7 0.65 ca
7 | Steel .. 42 6.0 0.80 128

The method of calibration adopted is as follows :

The spring to be calibrated is fastened at one end to the brass tube of the
Rolling Carriage and at the other to a fixed support. A string fastened to the end
of the shaft passes over a light, almost frictionless pulley, and carries a bag, in
which the weights are placed. The extensions of the spring are registered by
the pencil on the chronograph barrel. Settings are made on opposite sides of a
mean position, first, by letting the weight fall gradually to its lowest position ;
and, second, by extending it beyond its normal position and allowing the tension
of the spring to draw it back. In both cases a series of vibrations are sent
through the apparatus by the jar set up on the table, by means of a large tuning-
fork, so as to overcome the friction of the moving parts. In a portion of the
calibration experiments, these vibrations were produced by an electro-magnet.

96 EXPERIMENTS IN AERODYNAMICS.

The results of the calibration were plotted in curves, and these curves have
been used for translating all the spring extensions of the experiments into
pressures.

Three square planes were used, 6, 8, and 12 inches on a side, and in every
case the center of the plane was placed nine meters from the center of the
whirling-table. The air temperature was recorded at the beginning and end
of each series of observations. The average wind velocity was obtained from a
Casella air meter, which was read each day at the beginning and end of the
experiments. It should be noted that these wind velocities are valuable as indi-
cating the conditions of experiment, but do not afford any basis of correction to
the observations, since the method adopted in reading the trace eliminates the
effect of wind currents, so far as it is possible to do so. In a complete revolution
of the turn-table the arm during half of the revolution moves with the wind, and
during the other half moves against the wind; consequently the pressure will
be too great during the latter half and too small during the former half of the
revolution. Thus, if the velocity at the end of the arm be V, and the wind
velocity be v, the wind pressure at one point of the revolution will be propor-
tional to (V+ v)?, and at the opposite point will be proportional to(V —v). The
resulting trace, therefore, vibrates on either side of a mean position, and a line
drawn through the trace to represent this mean position gives a numerical value
that is larger than the pressure due to the velocity V in the ratio of V° + vw’ to V’.
But, in general, this error in reading the traces is quite negligible, and the average
mean position may be taken as reliable within the limits of accuracy imposed
on us. The spring extension adopted always refers to this mean position, and no
further correction is admissible. A specimen of the records of a series of experi-
ments is here given in detail, taken from the note book for October 25, 1888:

OctToBER 25, 1888.

Barometer, 738 mm.; mean temperature, 16°C. At 4.53 p. m., air meter, 416,445; at 5.25
p. m., air meter, 419,130. Eight-inch square wind-plane. Spring No. 1. Distance of center of
plane from axis of rotation, 9 meters.

First registering sheet. Four records at about 43 revolutions per minute. Ended at 4.05.
Almost a perfect calm. Velocity too small to get reliable spring extensions.

Second sheet started at 4.24 p.m. Two records at 10 revolutions per minute. Ended at
4.28 p.m. Pencil failed to make satisfactory record.

THE ROLLING CARRIAGE, ae

Third sheet started at 4.34 p.m. at nearly 14 revolutions per minute. Four records obtained.
Ended at 4.44 p. m.
Reading of traces.

Number of peconds Velocity PEREDICS OE Extension of spring Pressure on plane
in one revolution | plane (meters per) “yy, 4 (inches). — (pounds
of turn-table. | second). sly Sah See:
|
4.29 | 13.14 0.97 1,30
4.29 | 13. 0.75 1.10
4.58 12:93 | 0.82 1.15
4.38 12:93 | 0.78 U2

Fourth sheet. Velocity about 20 revolutions per minute. Two records obtained. Ended

at 4.57 p.m.
Reading of traces.

| |

| Extension of spring | Pressure on plane

l
+ | , .
Number of seconds | Velocity of center of

in one revolution | plane (meters per | “3 :

: | No. shes) eee (pounds).
| of turn-table. | second). | 0. 1 (inches) pounds)
| | |

oats ee | . -| = oe
2.88 19.60 | 2.33 | 2.55
2.90 19.50 2:28 2.51
|

Vifth sheet. Velocity about 25 revolutions per minute. Two records obtained. The first
record is good. The second record cannot be interpreted. Ended at at 5.15 p.m.

Reading of traces.

Number of seconds | Velocity of center of | Deaiemctom GP SNe Prescure! on plane |
% : , s s | Pressure 2
in one revolution | plane (meters per) ~~ No.1 Rs a one nee is 1 ae
aNO. 21es ). AS).
of turn-table. | second). | DEG pom

pee toee. = saad saree

2.45 | 23.10 3.76 3.90

The experiments were made from October 24 to November 2, 1888, with a
short series on November 28, 1890, and embrace observations with 6, 8, and 12
inch square planes, those with the 6-inch plane extending over velocities from 7
to 30 meters per second. They are presented in exrtenso at the end of the present
chapter The extension of the spring is given in inches, as originally measured
from the trace, and the corresponding pressures are given in pounds and
erammes. The next succeeding column gives the pressure P in grammes per
square centimeter of the wind-plane surface. The last column gives the value of
the coéfficient *,, in the equation P= *,, V*, where P is the pressure in grammes
on a square centimeter of surface, and V the velocity expressed in meters per
second. The subscript m is used here, as in previous chapters, to designate these
metric units.

One of the objects of the experiments was to test the generally accepted law,
that the pressure varies as the square of the velocity, and for this purpose

13

98 EXPERIMENTS IN AERODYNAMICS.

velocities were used ranging from 7 to 30 meters per second (11 to 67 miles per
hour). The mean of 10 observations with the 6-inch plane, at velocities between
25 and 30 meters per second, gave ,, = 0.0081; and the mean of 12 observations,
at velocities between 7.1 and 14.3 meters per second, gave the same value.
Therefore the departure from the law of the squares, if there be any between
these limits of velocity, is not sufficiently large to be detected by this apparatus.

If variations in the density of the air produced by changes of temperature
be considered in their effect upon the relation between pressure and velocity, the
preceding formula may be expressed in the form

re km V?
1 + .00366 (@ — 10°)’

where .00366 is the coéfficient of expansion of air per centigrade degree; ¢ is the
temperature of the air expressed in centigrade degrees, and £,, is the value of
the coéfficient for a standard temperature of 10°C. In the following summary,
all the values of #,, are collected and reduced by aid of this formula to a common
mean temperature of 10° C.; the values refer, also, toa mean barometric pressure
of 736 mm. An additional column is added, giving the corresponding value of
k in English measures for velocities expressed in feet per second and pressures in
pounds per square foot.

TABLE XVIII.

Summary of values of ktm obtained with the Rolling Carriage.

Number T ,
= : of ree sora ] km, k,
Size of plane. Deis obserya- ase ae tort —— 1 OP Cn eons — sO SIC?
tions. :
1888.
12 inches square. | Oct. 24 9 10.0 0.01027 0.01027
BBO 11 7.8 0.00913 0.00906
Noy. 2 1 19.0 0.0083 0.00859
1890.
| Nov. 28 3 — 2.0 0.00990 0.00948
Weighted mean....... 0.00944 0.00180
| 1888. ix as
6 inches square. | Oct. 24 3 10.0 0.00760 0.00760
| “ 29 6 12.0 0.00785 0.00790
Nov. 1 12 20.0 0.00810 0.00840
aed 13 19.0 0.00840 0.00867
Weighted mean........ | 0.008838 0.00159
| >
8 inches square. | Oct. 25 | 7 16.0 0.00754 | 0.00770 0.00147
General weighted mean. 0.0087 0,00166

THE ROLLING CARRIAGE. 99

The resulting values of /,, for the 6, 8, and 12 inch square planes are not
entirely accordant, as the successive sets of observations with the 12-inch plane
all give considerably larger values than those obtained with the smaller planes,
I am not disposed, however, to consider this as a real effect due to an actual
difference in the pressure per unit area on these planes. Such a difference, if one
exists, is in all probability quite small, and much within the degree of accuracy
possessed by these experiments. The resulting differences in the mean values of
k,, 1 consider, therefore, as discrepancies in the observations, the cause of which
has not become apparent. In recognition, however, of the fact that other experi-
menters have claimed to discover a difference in the pressure per unit area on
planes of different sizes, I have, in general, in the preceding chapters, taken pains
to specify the area of the plane to which all my experimental results apply.
That there should be a real, though perhaps a small, difference between the
pressure per unit area on planes of different sizes seems in fact quite probable,
when we consider that the ratio of perimeter to area varies for similar shaped
planes of different sizes. If the side of a square plane be @ and that of another

: : . - 4. 4.
be na, the ratio of perimeter to surface is ~ in the one case and || In the other,

which is not merely an expression of a mathematical relation, but calls attention
to a possibly important physical fact, for it seems probable that this relation
between perimeter and area has a considerable influence in determining the
pressure on the plane, especially that part of it produced by the diminution of
pressure on its posterior face.

The general weighted mean of all the values of #,, is 0087, or, in English
measures, & = .00166, and I believe this result is within 10 per cent. of the true
value. These experiments lead me to place the lymits of the value of /,, for a
1-foot square plane between 0.0078 (& = .0015) and 0.0095 (4 = .0018) for the
assumed temperature of 10° C., and pressure 736 mm., and, made as they were
in the open air and subject to wind currents, they are not sufficiently precise to
give more contracted limits. It may be noted that the value of /,, obtained from
the experiments with the Resultant Pressure Recorder, viz., k,, = .OO8O, falls
between the probable limits above assigned, and is within the probable uncertainty
(10 per cent.) of the mean of the results with the Rolling Carriage. The Rolling
Carriage, therefore, although a very sensitive and delicate piece of apparatus, has
not been able under the conditions of experiment to yield a sensibly better
result than the rougher instrument.

100 EXPERIMENTS IN AERODYNAMICS.
Measurement of wind pressure on normal planes by means of the Rolling Carriage.
Ocroper 24, 1888.
PRESSURE ON ONE-FOOT SQUARE PLANE (929 square centimeters).

Barometer, 735 mm.; mean temperature, 10°.0 C.; wind velocity, 2.8 meters per second.

ao
5

A Lo Bi tg:
5 as | ae Scie i Pressure en wind-plane.
3 Be 2g an |
& Sr dire ge. De |
3 a eee aS z
a 2 ie roleeas gS (grammes | km = —
= Oia Bo? ‘+z- ~~ (Pounds.) | (Grammes.) per is
2 aa S38 5S square
2 = 3 E ra = mG centimeter).
= Z i ; &
1.20 p.m. 14.00 13.18 3.39 3.59 1,610 1.73 0.0100
14.00 13.18 3.62 3.84 1,740 1.87 0.0108
1.40 p.m. | 949 8.92 1 aleyAl 776 0.83 0.0105
9.49 8.92 1.42 IegAal 776 0.83 0.0105
2.00 p.m. | 5,50 5.15 0.32 0.58 263 0.28 0.0107
5.60 5.28 0.30 0.53 240 0.26 0.0093
215 p.m. 14.90 14.08 3.90 3.99 1,810 1.95 0.0099
15.00 14.09 4.10 4.19 1,900 2.04 0.0104
14.80 13.91 4.00 4.08 1,850 1.99 0.0103
Mean =| 0.01027

PRESSURE ON SIX-INCH SQUARE PLANE (232 square centimeters).

a ae 2 80 .
3) SiS) aS a Pressure on wind-plane.
S ow er) es
3 SEs =a a2
> oe aae ao |
x nS 2 oN Gy re
5) ar Sy as o° 12
2) O55 wy a =| IP
= Claes 2 IRS) (grammes | k; =—
=) | = es) a 7 gYe m 72
¢ wHOoH ey, 2 hn o J
>= os G22 | ad (Pounds.) | (Grammes.) per
2 pen Sag B.S square
= Bn Oo see uA centimeter).
= v4 = S
4.00 p.m. 2.32 24.3 1:93 2.18 990 4.26 0.0072
2.52 23.8 Heo 2.22, 1,008 4,34 0.0077
2.52 23.8 2.05 2:29 1,040 4.48 0.0079
Mean=j| 0.0076

THE ROLLING CARRIAGE. LOL
October 25, 1888.
PRESSURE ON EIGHT-INCH SQUARE PLANE (413 square centimeters).

Barometer, 738 mm.; mean temperature, 16°.0 C.; wind velocity, 0.6 meter per second.

oO
3

Pressure on wind-plane.

s mo SS m

g Ze ae ay

= Sis =°e Biey

off fei tS fo nm oD

> oS 4 Last spore aes

fond (rd eee) =e eo

2 ae ST AS oy | 12 P

a Balch) SK a

= © Eee eI S ae (grammes | km = 7
: + ss = 7 pb 4 iS

b= Sa5 Boa ‘Zo (Pounds.) | (Grammes.) per

° icteaers 23 8 ae) square

a Bao | gaa GG centimeter).

S A = me

4.50 p.m. 4.26 13.14 0.97 1.80 590 1.45 0.0083
4.29 15.14 0.75 1.10 499 T21 0.0070
4.58 12.93 0.82 1.15 522 1.26 0.0075
4.58 12.93 0.78 1.12 508 1.23 0.0074
2.88 19.60 2.33 2.55 1,157 2.80 0.0073
2.90 19.50 2.28 2.51 1,139 2.76 0.0073
5.15 p. m. 2.45 23.10 35.16 3.90 1,770 4.29 0.0080

Mean = 0.00754

OcroBEeR 29, 1888.
PRESSURE ON SIX-INCH SQUARE PLANE (232 square centimeters).

Barometer, 735 mm.; mean temperature, 12°.0 C.; wind velocity at 1 p. m., 3.3 meters per second.

| as Bz op :

S sce Ae cele Pressure on wind-plane.

= ons 2 wan

S O50 Se Pc ;

= oO a! 4 ao = neo ]

a Te a ea wo

Oo aa} oC =) o°o | P

R Sa 2S cra a fs] } P

= 2 2 2 Sas as (grammes | kn = ie

= Sag ore | -cac (Pounds.) | (Grammes.) per

5 aos S8x Bo square

5 B-A Oo See | kG | centimeter).

E Z, > =

| (Noa a
4.24 p.m. 2.15 26.30 3.00 3.20 1459 6.25 0.0090
4.28 p.m. 2.03 27.85 3.08 3.26 1,480 6.38 0.0082
4.53 p.m. 1.88 30.15 3.41 3.57 1,620 | 6.98 0.0077
4.57 p.m. 1.95 29.20 3.19 3.39 1,520 6.55 0.0077
5.29 p. m. 4.29 13.20 0.36 0.61 277 IG; 0.0068
5.39 p.m. 3.95 14.30 | 0.50 0.80 363 1.57 0.0977
Mean =| 0.00785

102 EXPERIMENTS IN AERODYNAMICS.

Ocroper 30, 1888.
PRESSURE ON ONE-FOOT SQUARE PLANE (929 square centimeters).

Barometer, 739 mm.; mean temperature, 7°.8 C.; wind velocity, —.

mn Sam &N
a2 Ss a Pressure on wind-plane.
Oi. So | 5 a
S32 SEA | 2s
Bea) 6-2 |e p P
Santee Sia S ao (grammes | kn = =,
See Bog oa ha (Pounds.) | (Grammes.) per V
Te Og H Bo square
Ze 5 < A.B Lia centimeter).
Zz = g
7.23 7.84 0.88 1.20 544 0.58 0.0095
10.14 5.58 0.25 0.50 227 0.244 0.0079
7.89 alt/ 0.69 1.01 458 0.493 0.0096
10.86 5.22 0.27 0.51 231 0.249 0.0092
11.52 5.00, 0.28 0.52 236 0.254 0.0102
8.56 6.62 0.47 0.75 340 0.366 0.0084
6.64 8.51 1.00 1.30 589 0.634 0.0088
6.74 8.59 1.00 1.30 589 0.634 0.0090
6.30 8.98 1.33 1.62 734 0.790 0.0098
6.20 Shi? a3} 1.63 739 0.796 0.0096
5.93 9.54 127 1.56 707 0.761 0.0084
Mean=) 0.00915

NoveMBer 1, 1888.
PRESSURE ON SIX-INCH SQUARE PLANE (232 square centimeters).

Barometer, 741 mm.; mean temperature, 20°.0 C.; wind velocity, 1.5 meters per second.

S m wie op 2

3 ee 9 a. Pressure on wind-plane.

= SB gy 22 ae

a ee | gee | a8

2 yo | ae Se P

= SAT S= 9 ES | (grammes) | kin = 2

3 SEs Beg mes (Pounds.) | (Grammes.) | per A

PS rte a5 Sas BS square

q 5-0 SAA Tae centimeter).

SI A > ia)

3.30 p.m. 4.35 13.00 1.60 0.78 356 1.53 0.0091
4.32 13.10 1.48 0.70 820 1.38 0.0080
3.99 14.20 2.19 1.04 472 2.03 0.0100
4.00 14.14 2.07 0.99 449 1.93 0.0096
4.00 14.14 1.60 0.78 356 1.53 0.0077
3.96 14.80 1.58 0.78 854 1.53 0.0075
5.64 10.00 0.64 0.36 163 0,70 0.0070
5.67 297, 0.61 0.35 159 0.69 0.0069
5AO 10.47 0.80 0.48 INS 7/ 0.85 0.0077
5.51 10.26 0.69 0.38 174 0.75 0.0071
(93 7.13 0.30 0.20 91 0.38 0.0077
5.25 p.m. 7.60 7.44 0.40 0.25 113 OAD 0.0089
Mean = | 0.00810

Barometer, 735.6 mm.

THE ROLLING CARRIAGE,

Novemser 2, 1888.

PRESSURE ON SIX-INCH SQUARE PLANE (232 square centimeters).

103

; mean temperature, 19°.0 C.; wind velocity, 1.5 meters per second.

ad Soak on :
§ a3 = 3 43. Pressure on wind-plane.
~ ons oD aa
3S oF 3 Bie om SS = a
F Mees SER aoe
3 BEd os Sai P
a Sa OG en. 2 q P
= ose Oo RSP (grammes | km = —,
cu Hos Ao od 3 1 ql “(5 ees V?
a Ses Qa a (Pounds.) | (Grammes.) per
o Fal aie Sis 5 BS | square
a 5 isis) ie oz centimeter).
i= ZA - ea)
11.00 a. m. 2.14 26.40 2.92 3.11 1411 6.08 0.0087
2.13 26.55 2.62 2.85 1,294 5.56 0.0079
2.45 23.30 2.27 2.52 1,143 4.92 0.0091
2.73 20.70 1.80 2.10 953 4.10 0.0096
2.91 19.40 132 1.67 758 3.26 0.0087
5.66 10.00 0.16 0.45 204 0.88 0.0088
3.72 15.20 0.52 0.90 408 1.76 0.0076
3.62 15.60 0.53 0.91 413 LTRS) 0.0073
3.10 18.20 iLaly) 1.54 699 3.01 0.0091
2.03 27.85 3.49 3.63 1,646 7.09 0.0091
2.03 27.80 3.08 3.27 1,484 6.58 0.0083
IS) 28.40 3.00 3.19 1,448 6.22 0.0077
1.94 29.10 2.84 3.04 1,380 5.95 0.0070
Mean =| 0.0084
PRESSURE ON ONE-FOOT SQUARE PLANE (929 square centimeters).
Note: Wind too high for best results.
Z m4 sale ap :
a) ee Ee asia Pressure on wind-plane.
3 SB sg Ze en
z oS eee oe a P
2 5 F a S= 8 gc (grammes | kn = pe
o Sas Pee os (Pounds.) | (Grammes.) | per
5) ‘a oe oa k aS square
ai 5-H Oo a ee tea centimeter).
is Za S eS
1.50 p.m. 2.27 24.9 2.28 10.60 4,810 5.18 0.0084
2.34 24.1 1.92 9.05 4.105 4.42 0.0076
2.90, 19.5 1.28 6.25 2,835 3.05 0.0080
3.10 18.2 1.27 6.20 2,810 3.03 0.0092
Mean =| 0.0083

104 EXPERIMENTS IN AERODYNAMICS.

NoveMBER 28, 1890.
PRESSURE ON ONE-FOOT SQUARE PLANE (929 square centimeters).

Barometer, 737 mm.; mean temperature, — 2°.0 C.; wind velocity, 1.2 meters per second.

Pressure on wind-plane.

P
(grammes | km =-—
(Pounds.) | (Grammes.) per

square
centimeter).

Time of observation.
Number of seconds
in one revolution
of turn-table.
Velocity of center of
plane V (meters
per second).
Extension of spring
No. 1 Ginches).

0.0099
- 0.0099
0.0099

emt
eupen
oO
Ro)
o>
ey
bo
(94)
=)

Ou
oO 0
yen
wo
iw)
i
(S)
trywt
er
oS
Hee
Foe he
oo ho Go
ea

pes
a
Or
ho
is
(0/4)

NS)
So
nw

CHAPTER X.

SUMMARY.

The essential feature of the present work has been the insistance on the
importance of a somewhat unfamiliar idea—that rapid aerial locomotion can be
effected by taking advantage of the inertia of the air and its elasticity. Though
the fact that the air has inertia is a familiar one, and though the flight of certain
missiles has indicated that this inertia may be utilized to support bodies in rapid
motion, the importance of the deductions to be made has not been recognized.
This work makes the importance of some of these deductions evident by experi-
ment, and perhaps for the first time exhibits them in their true import.

This memoir is essentially a presentation of experiments alone, without
hypotheses, and with only such indispensable formule as are needed to link the
observations together. These experiments furnish results which may be suc-
cinctly summarized as follows :

The primary experiment with the Suspended Plane is not intended per se
to establish a new fact, but to enforce attention to the neglected consequences of
the fundamental principle that the pressure of a fluid is always normal to a
surface moving in it, some of these consequences being (1) that the stress neces-
sary to sustain a body in the air is less when this is in horizontal motion than
when at rest; (2) that this stress instead of increasing, diminishes with the
increase of the horizontal velocity (a fact at variance with the conclusions of
some physicists of repute and with ideas still popularly held); (8) that it is at
least probable that in such horizontal flight up to great velocities the greater the
speed the less the power required to maintain it, this probability being already
indicated by this illustrative experiment, whi'e demonstrative evidence follows
later.

The experiments which are presented in Chapter IV result in an empirical
curve, giving the ratio between the pressure on an inclined square plane and
on a normal plane moving in the air with the same velocity. Incidentally it
is shown that the pressure is normal to the inclined surface, and hence that the
effects of skin-friction, viscosity, and the like are negligible in such experiments.
It is also shown that for the small angles most used in actual trial of the plane, the
pressure on it is about 20 times greater than that assignable from the theoretical
formula derived from Newton’s discussion of this subject in the Principia. This

14 (105)

106 EXPERIMENTS IN AERODYNAMICS.

last experimental result is not presented as a new contribution to knowledge,
since it had previously been obtained by experimenters in the early part of this
century; but as their results appear not to have met with the general attention or
acceptance they deserve, it is not superfluous either to produce this independent
experimental evidence or to urge its importance.

The experiments with the Plane-Dropper introduce matter believed to be
novel as well as important. They show (1) that the time of falling of a hori-
zontal plane is greater when moving horizontally than when at rest, and (2) that
this time of falling most notably increases with the velocity of lateral translation ;
(3) experiments with different horizontal planes show that this increase in the time
of falling is greater for those planes whose extension from front to back is small
compared with their length measured perpendicular to the line of advance ;
(4) the horizontal velocities are determined at which variously shaped inclined
planes set at varying angles can soar—that is, just sustain their own weight in
the air under such cireumstances—and these data afford the numerical basis
for the important proposition that the power required to maintain the horizonta!
motion of an inclined aeroplane is less for high speeds than for low ones ; (5) by
experiments with double planes, one above the other, it is shown that planes of
the advantageous shape mentioned above, do not interfere with each other at
specified speeds, if so placed at an interval not less than their length from front
to back ; and it is pointed out that an extension of this method enables us to
determine the extent to which any underlying air stratum is disturbed during
the plane’s passage.

Chapter VI contains further data, which confirm the important conclusions
derived from the experiments with the Plane-Dropper, already cited, and some
results on the pressures on inclined planes having different “ aspects” with refer-
ence to the direction of motion are also presented, which are believed to be new
and of importance. Further chapters present experiments with a special instru-
ment called the Dynamometer-Chronograph and with other apparatus, which
give data regarding aerial propellers, a series of experiments on the center of
pressure of moving planes, and another series upon the pressure on a normal
plane.

The conclusions as to the weights which can be transported in horizontal
flight have included the experimental demonstration that the air friction is
negligible within the limits of experiment. It has not been thought necessary
to present any evidence that an engine or other adjunct which might be applied
to give these planes motion, need itself oppose no other than frictional resist-
ance, if enclosed in a stream-line form, since the fact that such forms oppose
no other resistance whatever to fluid motion, has been abundantly demonstrated
by Froude, Rankine, and others.

SUMMARY. 107

The most important general inference from these experiments, as a whole,
is that, so far as the mere power to sustain heavy bodies in the air by mechanical
flight goes, such mechanical flight is possible with engines we now possess, since
effective steam-engines have lately been built weighing less than 10 pounds to
one horse-power, and the experiments show that if we multiply the small planes
which have been actually used, or assume a larger plane to have approximately
the properties of similar small ones, one horse-power rightly applied, can sustain
over 200 pounds in the air at a horizontal velocity of over 20 meters per second
(about 45 miles an hour), and still more at still higher velocities. These numer-
ical values are contained in the following table, repeated from p. 66. It is scarcely
necessary to observe that the planes have been designedly loaded, till they weighed
500 grammes each, and that such a system, if used for actual flight, need weigh
but a small fraction of this amount, leaving the rest of the sustainable weight
indicated, disposable for engines and other purposes. I have found in experiment
that surfaces approximately plane and of 7; this weight are sufficiently strong for
all necessary purposes of support.

Data for soaring of 830 x 4.8 inch planes ; weight, 500 grammes.

| Weight with planes of like
ice: , Work expended per min- form that 1 horse-power
Soar xp I 3 ; I]
Nae “itl Poammexepeed 7 ute. will drive through the
ngle with air at velocity V.
horizon a. 4 ‘
Meters per | Feet persec-| Kilogram- : Kilo-
second. ond. meters. Foot-pounds. grammes. OEERES.
45 11.2 26.7 33 2,48 6.8 15
3 10.6 3458 175 1,268 13.0 29
15 11.2 36.7 86 623 26.5 58
10 12.4 40.7 65 474 34.8 77
5 15.2 49.8 41 297 55.5 122
2 20.0 65.6 24 174 95.0 209

I am not prepared to say that the relations of power, area, weight, and
speed, here experimentally established for planes of small area, will hold for
indefinitely large ones; but from all the circumstances of experiment, I can
entertain no doubt that they do so hold far enough to afford assurance that we
can transport, (with fuel for a considerable journey and at speeds high enough to
make us independent of ordinary winds,) weights many times greater than that
of a man.

In this mode of supporting a body in the air, its specific gravity, instead of
being as heretofore a matter of primary importance, is a matter of indifference,
the support being derived essentially from the inertia and elasticity of the air on
which the body is made to rapidly run. The most important and it is believed

108 EXPERIMENTS IN AERODYNAMICS.

novel truth, already announced, immediately follows from what has been shown,
that whereas in land or marine transport increased speed is maintained only by
a disproportionate expenditure of power, within the limits of experiment in such
aerial horizontal transport, the higher speeds are more economical of power than the
lower ones.

While calling attention to these important and as yet little known truths, I
desire to add as a final caution, that I have not asserted that planes such as are
here employed in experiment, or even that planes of any kind, are the best forms
to use in mechanical flight, and that I have also not asserted, without qualification,
that mechanical flight is practically possible, since this involves questions as to
the method of constructing the mechanism, of securing its safe ascent and descent,
and also of securing the indispensable condition for the economic use of the power
I have shown to be at our disposal—the condition, I mean, of our ability to guide
it in the desired horizontal direction during transport,—questions which, in my
opinion, are only to be answered by further experiment, and which belong to the
inchoate art or science of aerodromics, on which I do not enter.

I wish, however, to put on record my belief that the time has come for
these questions to engage the serious attention, not only of engineers, but of
all interested in the possibly near practical solution of a problem, one of the
most important in its consequences, of any which has ever presented itself in
mechanics ; for this solution, it is here shown, cannot longer be considered beyond
our capacity to reach.

}
|
i
|

APPENDIX A.

I append here the results of some additional experiments made with the Plane- Dropper
to determine the law of falling of a horizontal plane haying a horizontal velocity of transla-
tion. It will be recalled that the preceding data given in the chapter on the Plane-Dropper
show only the total time of falling a distance of four feet, and that we cannot determine
from it the law of fall, unless we know, in addition, the relative diminution in the accelera-
tion during the descent, and whether at the end of the fall the plane has attained an
approximately constant velocity. For high horizontal velocities and for the most adyan-
tageous planes, it is not impossible that an approximately constant velocity is reached within
the four-foot fall of the Plane-Dropper. In order to obtain these additional data, I placed
electric contacts upon the Plane-Dropper at intervals of every foot, and introduced other
modifications into the method of experiment. The accuracy with which it was necessary
to measure the relative times of fall through successive feet precluded the further use of the
stationary chronograph for the registration, and I adapted a Konig chronoscope to this
purpose.

This chronoscope consists of a tuning-fork of low pitch, which is made to vibrate by
the action of an electro-magnet. The vibrations are registered by a pen-point on a strip of
paper covered with lamp-black, which is passed over a roller during the time of fall. A
second pen-point worked by an electro-magnet records the passage of the falling-piece over
the five successive contact-pieces of the Plane-Dropper. On the same strip, therefore, we
have the relative intervals between the successive contacts, and a time-scale for their
evaluation. Although not essential for the evaluation of the intervals, approximate
uniformity in the motion of the strip of paper was obtained by fastening to the ends brass
clips differing suitably in weight, and converting this part of the apparatus into an Atwood’s
machine.

Two separate batteries were used, an electropoion battery of four cells, equivalent to
thirty or forty Daniel’s cells, for vibrating the tuning-fork, and an ordinary battery of eight
cells for the Plane-Dropper and the quadrant contacts of the turn-table. The current from
this battery is forked into two branches, one branch running to the quadrant contacts of the
turn-table and to the observatory chronograph on which they register; the other branch,
going to the Plane-Dropper, actuates the release magnet, passes through the five electric
contacts, and thence goes to the electro-magnet on the Kénig chronoscope, where these
contacts are registered, and finally back to the battery. This circuit is closed by a make-
key in the hands of the operator at the chronoscope.

A preliminary calibration of the tuning-fork was made by connecting one pen of the
chronoscope with the mean time-clock, and obtaining a number of strips containing both
second intervals and tuning-fork vibrations.

(109)

110 EXPERIMENTS IN AERODYNAMICS.

Calibration of tuning-fork.
DecemBer 12, 1890.—G. E. Curtis, Observer.

Temperature of tuning-fork, 18° C.

Number of vibrations of fork per second.
Number of |
strip. l 9
Ist second. 2d second. x mare a
SL |e | eee ee 49.9
3 48.6
4 48.2 51.9
47.8
5 48.8 51.0
48.6 50.8
48.5

Mean, 49.9 vibrations per second.

The measurement of the strips showed that the clock was not “on beat,” and that two
successive seconds must be taken in order to get the true interval. The mean of the
measurements gave 49.9 vibrations per second. The tuning-fork was evidently constructed
to give 50.0 vibrations per second, and this value was therefore adopted. The fraction of
a vibration can be accurately estimated to tenths; hence the instrument, as used in these
observations, gave time intervals to 45 part of a second, which is sufficiently accurate for
the purpose.

Preliminary experiments were made with the Plane-Dropper at rest indoors for the
purpose of testing the new contacts and the Kénig registration apparatus. The pair of
12 x 6 inch planes were fastened horizontally to the falling piece. Then the observer, with
one hand, sets in motion the blackened strip on the Konig, and with the other, immediately
thereafter, presses the make-key, which operates the release magnet of the Plane-Dropper.
The blackened strip containing the registration is then passed through a solution of shellac
and ammonia, by which the trace is permanently set.

The result of these preliminary experiments is as follows:

Time of fall of pair of 12 x 6 inch planes, horizontal.

December 10, 1890.—G. E. Curtis, Observer.

ie , Ree

Observed time of | Theoretical time | 7),

| fall (seconds). | (in vacuo). Difference.
IAS Hh (Of8\ ee Se i | 0.220 | 0.250
QObLOO een ce aaa mate 0.110 | 0.104 + .006
Ric Mey} hae ee eee 0.090 | 0.080 O10
Bthifoots eee eee ee 0.080 0.066 + 014

Motalvasfeetee= aeaee oe 0.500 0.500

APPENDIX A. ali

The first contact is not at absolute rest, but a fraction (0.4 or 0.5) of an inch below the
position of rest; hence, when it records, the plane has already attained a small velocity.
To this is due the fact that the time of falling the first foot, which is registered by the first
and second contacts, is less than the computed time in vacuo by .03 second. At least this
amount should therefore be added to the observed time for the first foot, and the total time
will be 0.53 seconds. This gives a total retardation of 0.03 seconds, due to the resistance of
the air. Attention is called to the symmetrical character of the differences between the
observed and the computed time in vacuo, showing the increasing retardation corresponding
to increasing velocities of fall. Being assured by these results of the perfect adaptation of
the apparatus to secure the desired data, the Plane-Dropper was placed upon the whirling-
table December 13, 1890.

When the whirling-table has attained uniform motion at the speed desired, a signal is
given to the observer seated at the Konig chronoscope to proceed with the experiment.
First, by a break-key he cuts out for a moment the quadrant contacts as an evidence on
the chronograph sheet of the time of the experiment. Second, the chronoscope strip, which
has previously been prepared and placed upon the roller, is set in motion by the release of
a detent, and an instant later, when the strip has gotten fully into motion, the make-key of
the Plane-Dropper circuit is pressed, releasing the falling plane. As the falling plane passes
each of the five contact pieces the circuit is completed, and registration is made upon the
Konig strip. In two seconds after setting in motion the Konig strip the experiment is at
anend. The strip containing the record is then passed through the solution of shellac and
alcohol for setting the trace, after which it is measured at leisure. Meanwhile a new strip
is placed upon the chronoscope, and the apparatus is in readiness for another trial.

The results of the observations covering a range of horizontal velocity from 6 to 26
meters per second (13.5 to 58.5 miles per hour) are contained in the accompanying table.

To find the times of falling successive feet of planes having a horizontal velocity.
DrceMBER 13, 1890.

F. W. Very, G. E. Curtis, Observers.

One pair 12 x 6 inch planes horizontal; weight, 464 grammes (1.02 lbs.); mean temperature, 0° C.; wind
velocity, 1.85 meters per second.

TIMES OF FALL AT DIFFERENT HORIZONTAL VELOCITIES.

Horizontal
velocity as vA | 5 5) | 7 | 29 | 997 | 989
(meters per At rest. 6.0 | 11.9 12.0 12.1 14.6 144 18.0 22.1 | 26.2
second). | |
| | |
list foot)--==—-=- 0.218 0.314 | 0.284 | 0.389 | 0.429 | 0.834 0.448 | 0.678 | 0.930 | 0.600 | 1440 | 0.962
2OtoOb=aa == | LOTTA) O20) 5) ONE O25) OL257 |) 10:2 | 0.147 | 0.202 | 0.450 | 0.220 | 0.285 | 0.303
SOd0Obe === == 0.089 | 0.094 | 0.088 | 0.105 |------- B24 0.166 | 0.360 | 0.306 | 0.340 | 0.280 | 0.399
4th foot---- ---- 0.079 | 0.082'| 0.077 | 0.098 |------- 5 O90 5 pee Sane OS0) ea | C0457)
} |e ee = Se | a = = A gas
Total, 4 feet--| 0498 | 0.610 | 0.560 | 0.717 |-----.- ag etre {Oe SL | = Ne ee 1.340 | 2.005 | 2.151
| | | |

* Seriously affected by wind.
y 3

112 EXPERIMENTS IN AERODYNAMICS.

SUMMARY.
Velocity (meters | Time of falling | Increase over time
per second). 4 feet. in vacuo.
0.0 0.55 0.05
6.0 0.72 0.22
12.0 0.95 0.45
18.0 1.54 0.84
22.0 2.00 1.50
26.0 2.15 1.65

The time of falling the total 4 feet increases from 0.55 second, when the plane is at
rest, to 2.15 seconds, when the plane has a horizontal velocity of 26 meters per second.
Examining the time of falling the several successive feet, it will be seen that there is no
uniformity in the relative times in which the several distances were passed over. Only the
first experiment at 6 meters per second shows a velocity of fall continually increasing at a
diminishing rate as the circumstances require. The remaining four experiments, for which
a complete record was obtained, show decreasing velocities of fallin a part or all of the
distance after the first foot. These anomalous and discordant results are in all probability
due to wind currents having a vertical component, which vitiated the observations. Thus
the completeness of the apparatus and the perfection of the details of operations, whereby
an accuracy of 4, of a second was secured, were all rendered futile by the uncontrolled
conditions under which the experiment was unavoidably conducted, and no decisive result
was added to those already summarized.

APPENDIX B.

Mr. G. E. Curtis calls my attention to the fact that the conclusion that the power
required to maintain the horizontal flight of an aeroplane diminishes with the increasing
speeds that it attains, may be deductively shown by the following analysis:

Representing the work to be done per second by 7, the resistance to horizontal motion
by R, and the horizontal yelocity by V, we have by definition

T= RV.

Substituting for R its value, W tana (see p. 65), W being the weight of the plane, we
have the equation
T = VW tan a,

in which «and V are dependent variables. The curves of soaring speed (Fig. 9) enable

us, in the case of a few planes, to express « in terms of V, but, for any plane and without

actually obtaining an analytical relation between V and «, we may determine the character

of the function 7, i. ¢., whether it increases or decreases with V, in the following manner:
Differentiating with respect to V, we obtain

le
a i (tan a + V sec? ‘i av ‘

Now, since in flight 2 is a very small angle, tan « will be small as compared with the

da : 5 ChGi <0 : = eh Ue

term V sec? a avai Hence the sign of the latter factor 77, will control the sign of Vv
: On eee ChE % ; ‘ da

Now, since V increases as « diminishes, ay 38 negative, which makes the term V sec? a TV

negative, and therefore, in general, 7 is a decreasing function of V. In other words,
neglecting the skin friction and also any end pressure that there may be on the plane, the
work to be done against resistance in the horizontal flight of an inclined plane must
diminish as the velocity increases.

15 ; (113)

APPENDIX C.

At the time of my experiments.to determine the varying position of the center of
pressure on an inclined plane moving in the air, I was unacquainted with the similar
experimental work of Joéssel* and of Kummer+ in the same field. Joéssel, who appears
to be the first experimenter on the subject, found for a square plane of length ZL that, as
the angle between the plane and the current is diminished, the center of pressure approaches
a point + Z from the forward edge, and that its position for any angle « between the plane
and the current may be represented by the formula

= (0.3 — 0.8 sin z) L,

d being the distance of the center of pressure from the center of plane.

The method of experiment adopted by Kummer is essentially similar to the one pur-
sued by me in the use of the Counterpoised Eccentric Plane. The object is to determine the
position of the center of pressure corresponding to different angles of inclination of a plane
to the current. The method pursued both by Kummer and myself has been the one which
most naturally suggests itself to find the angle of inclination « of the plane corresponding
to a series of fixed distances d of the center of pressure from the center of figure. Thus in
the experiments, d has been the independent variable, while in the use of the results, « is
in general the independent variable.

For a square plane 90 mm. (3.54 inches) on the side, Kummer obtained the following
results, which may be compared with the results given here in chapter VIII and with the
formula of Joéssel :

Distance of center | Distance as a per- : me
of pressure from centage of aide of | Angle ob plane with
center of plane. plane. Current.

mm. A
0 0.000 90
1 0.011 S4
2 0.022 77
3 0.033 7
4 0.044 62
3) 0.056 52
6 0.067 41
i 0.078 31
8 0.089 28
9 0.100 263

10 0.411 25
13 0.144 21
14 0.156 19
15 0.167 18

*Mémorial du Génie Maritime, 1870.

} Berlin Akad-Abhandlungen, 1875, 1876.
(114)

APPENDIX C. 11115)

In addition to determining the position of the center of pressure for a square plane,
Kummer extended his experiments to the case of differently shaped rectangles, and his
results with these are strikingly suggestive. It has been pointed out in chapter VI that
above and below an angle of about 30° there is a reversal in the relative amounts of the
pressure on inclined rectanglar planes of different shapes; the tabulated results of Kummer
exhibit a similar reversal in the position of the center of pressure, of which the following
may be given as an example:

Distance of center of pressure from center of plane.

Angles between plane and current. |
Size of plane.
45°. | 10°.

mm. mm. | mm.
180 x 180 11 40
90 x 180 14 36

For small angles the position of the center of pressure is further from the center of
figure in the 180 x 180 mm. plane than in the 90 x 180 mm. plane, while for 45° this
relation is reversed. It appears, therefore, that the reversal in the amount of pressure,
brought out in the experiments presented in this memoir, finds its counterpart in a corre-
sponding reversal in the position of the center of pressure exhibited in the work of Kummer.
It is believed that in this striking analogy may be found a key to the more complete
rational and deductive treatment of these inseparably related problems.

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE.
854

Spas.

RNa cE iN ic WORK

OF:

a ieee IND:

BY

Sob SANGER Y:

CITY OF WASHINGTON :
PUBLISHED BY THE SMITHSONIAN INSTITUTION.
1893.

(REPRINTED 1908 WITH APPENDIX FROM FRENCH EDITION OF 1893.)

Printed and Bound by
The Knickerbocker Press, Rew Work
G. P, Putnam’s Sons

ADVERTISEMENT

In conformity with the established practice of the Institution to
obtain the judgment of disinterested experts as to the propriety of
accepting Memoirs proposed for the Series of ‘Smithsonian Con-
tributions to Knowledge,” the accompanying paper has been
referred to a Commission consisting of Professors Simon Newcomb,
of the U. S. Nautical Almanac, Thomas C. Mendenhall, of the U. S.
Coast and Geodetic Survey, and Mark W. Harrington, of the U. S.
Weather Bureau ; and has received their approval and recommendation

for publication.

Wasuincton : December, 1893.

iii

rte Ne ENA LO WORK OP TEE WIND;

RAK ai:

INTRODUCTORY,

Tt has long been observed that certain species of birds maintain themselves
indefinitely in the air by “soaring,” without any flapping of the wing, or any
motion other than a slight rocking of the body; and this, although the body in
question is many hundred times denser than the air in which it seems to float with
an undulating movement, as on the waves of an invisible stream.

No satisfactory mechanical explanation of this anomaly has been given, and
none would be offered in this connection by the writer, were he not satisfied that
it involves much more than an ornithological problem, and that it points to novel
conclusions of mechanical and utilitarian importance. They are paradoxical at first
sight, since they imply that, under certain specified conditions, very heavy bodies
entirely detached from the earth, immersed in, and free to move in, the air, can be
sustained there indefinitely, without any expenditure of energy from within.

These bodies may be entirely of mechanical construction, as will be seen later,
but for the present we will continue to consider the character of the invisible sup-
port of the soaring bird, and to study its motions, though only as a pregnant
instance offered by Nature to show that a rational solution of the mechanical
problem is possible.

Recurring, then, to the illustration just referred to, we may observe that the
flow of an ordinary river would afford no explanation of the fact that nearly inert
creatures, while free to move, although greatly denser than the fluid, yet float upon
it; which is what we actually behold in the aérial stream, since the writer, like
others, has satisfied himself, by repeated observation, that the soaring vultures and
other birds appear as if sustained by some invisible support, in the stream of air,

* This paper was read by title to the National Academy of Sciences in April, 1893, and in full
before the International Conference on Aérial Navigation at Chicago in August, 1893.

2 THE INTERNAL WORK OF THE WIND.

sometimes for at least a considerable fraction of an hour. It is frequently sug:
gested by those who know these facts only from books, that there must be some
quivering of the wings, so rapid as to escape observation. Those who do know them
from observation, are aware that it is absolutely certain that nothing of the kind
takes place, and that the birds sustain themselves on pinions which are quite
rigid and motionless, except for a rocking or balancing movement involving
little energy.

The writer desires to acknowledge his indebtedness to that most conscientious
observer, M. Mouillard,* who has described these actions of the soaring birds with
incomparable vividness and minuteness, and who asserts that they, under certain
circumstances, without flapping their wings, rise and actually advance against
the wind.

To the writer, who has himself been attracted from his earliest years to the
mystery which has surrounded this action of the soaring bird, it has been a subject
of continual surprise that it has attracted so little attention from physicists. ‘That
nearly inert bodies, weighing from 5 to 10, and even more, pounds, and many hun-
dred times denser than the air, should be visibly suspended in it above our heads,
sometimes for hours at a time, and without falling,—this, it might seem, is, without
misuse of language, to be called a physical miracle; and yet, the fact that those
whose province it is to investigate nature, have hitherto seldom thought it deserving
attention, is perhaps the greater wonder.

This indifference may be in some measure explained by the fact that the
largest and best soarers are of the vulture kind, and that their most striking evolu-
tions are not to be seen in those regions of the Northern Temperate Zone where
the majority of those whose training fits them to study the subject are found.
Even in Washington, however, where the writer at present resides, scores of great
birds may be seen at times in the air together, gliding with and against the wind,
and ascending higher at pleasure, on nearly motionless wings. “Those who have
not seen it,” says M. Mouillard, “when they are told of this ascension without the
expenditure of energy, are always ready to say, ‘but there must have been move-
ments, though you did not see them,’”; “and in fact,” he adds, “ the casual witness
of a single instance, himself, on reflection, feels almost a doubt as to the evidence
of his senses, when they testify to things so extraordinary.”

Quite agreeing with this, the writer will not attempt any general description
of his own observations, but as an illustration of what can sometimes be seen, will
give a single one, to whose exactness he can personally witness. ‘The common

*L. P. Mouillard, Z’ Empire de 7’ Air, Paris ; G. Masson.

THE INTERNAL WORK OF THE WIND. 3

“Turkey Buzzard ” (Cathartes aura) is so plenty around the environs of Washing.
ton that there is rarely a time when some of them may not be seen in the sky,
gliding in curves over some attractive point, or, more rarely, moving in nearly
straight lines on rigid wings, if there be a moderate wind. On the only occasion
when the motion of one near at hand could be studied in a very high wind, the
author was crossing the long “ Aqueduct Bridge” over the Potomac, in an unusu-
ally violent November gale, the velocity of the wind being probably over 35
miles an hour. About one third of the distance from the right bank of the river,
and immediately over the right parapet of the bridge, at a height of not over 20
yards, was one of these buzzards, which, for some object which was not evident,
chose to keep over this spot, where the gale, undisturbed by any surface irregulari-
ties, swept directly up the river with unchecked violence. In this aérial torrent,
and apparently indifferent to it, the bird hung, gliding, in the usual manner of its
species, round and round, in a small oval curve, whose major axis (which seemed
toward the wind) was not longer than twice its height from the water. The bird
was therefore at all times in close view. It swung around repeatedly, rising and
falling slightly in its course, while keeping, as a whole, on one level, and over the
same place, moving with a slight swaying, both in front and lateral direction, but
in such an effortless way as suggested a lazy yielding of itself to the rocking of
some invisible wave.

It may be asserted that there was not only no flap of the wing, but not the
quiver of a wing feather visible to the closest scrutiny, during the considerable
time the bird was under observation, and during which the gale continued. A
record of this time was not kept, but it at any rate lasted until the writer, chilled
by the cold blast, gave up watching and moved away, leaving the bird still floating,
about at the same height in the torrent of air, in nearly the same circle, and with
the same aspect of indolent repose.

If the wind is such a body as it is commonly supposed to be, it is absolutely
impossible that this sustentation could have taken place in a horizontal current any
more than in a calm, and yet that the ability to soar is, in some way, connected with
the presence of the wind, became to the writer as certain as any fact of observation
could be, and at first the difficulty of reconciling such facts (to him undoubted)
with accepted laws of motion, seemed quite insuperable.

Light came to him through one of those accidents which are commonly found
to occur when the mind is intent on a particular subject, and looking everywhere
for a clue to its solution.

In 1887, while engaged with the “ whirling-table ” in the open air at the Alle-

gheny Observatory, he had chosen a quiet afternoon for certain experiments, but in

4 THE INTERNAL WORK OF THE WIND.

the absence of the entire calm which is almost never realized, had placed one of
the very small and light anemometers made for hospital use, in the open air, with
the object of determining and allowing for the velocity of what feeble breeze
existed. His attention was called to the extreme irregularity of this register, and
he assumed at first that the day was more unfavorable than he had supposed. Sub-
sequent observations, however, showed that when the anemometer was sufficiently
light and devoid of inertia, the register always showed great irregularity, especially
when its movements were noted, not from minute to minute, but from second to
second.

His attention once aroused to these anomalies, he was led to reflect upon
their extraordinary importance in a possible mechanical application. He then de-
signed certain special apparatus hereafter described, and made observations with
it which showed that “wind” in general was not what it is commonly assumed to
be, that is, air put in motion with an approximately uniform velocity in the same
strata; but that, considered in the narrowest practicable sections, wind was always
not only not approximately uniform, but variable and irregular in its movements
beyond anything which had been anticipated, so that it seemed probable that the
very smallest part observable could not be treated as approximately homogeneous,
but that even here, there was an internal motion to be considered, distinct both
from that of the whole body, and from its immediate surroundings. It seemed to
the writer to follow as a necessary consequence, that there might be a potentiality
of what may be called “internal work” * in the wind.

On further study, it seemed to him that this internal work might conceivably
be so utilized as to furnish a power which should not only keep an inert body from
falling, but cause it to rise, and that while this power was the probable cause of the
action of the soaring bird, it might be possible through its means to cause any
suitably disposed body, animate or inanimate, wholly immersed in the wind, and
wholly free to move, to advance against the direction of the wind itself. By this it
is not meant that the writer then devised means for doing this, but that he then
attained the conviction both that such an action involved no contradiction of the
laws of motion, and that it was mechanically possible (however difficult it might
be to realize the exact mechanism by which this might be accomplished).

It will be observed that in what has preceded, it is intimated that the difficul-

* Since the term “internal work” is often used in thermo-dynamics to signify molecular
action, it may be well to observe that it here refers not to molecular movements, but to pulsations
of sensible magnitude, always existing in the wind, as will be shown later, and whose extent and
extraordinary possible mechanical importance it is the object of this research to illustrate. The
term is so significant of the author’s meaning that he permits himself the use of it here, in spite of
the possible ambiguity.

THE INTERNAL WORK OF THE WIND. 5

ties in the way of regarding this, even in the light of a theoretical possibility, may
have proceeded, with others as with the writer, not from erroneous reasoning, but
from an error in the premises, entering insidiously in the form of the tacit assump-
tion made by nearly all writers, that the word “ wind” means something so simple,
so readily intelligible, and so commonly understood, as to require no special defini-
tion ; while, nevertheless, the observations which are presently to be given, show
that it is, on the contrary, to be considered as a generic name for a series of infinitely
complex and little known phenomena.

Without determining here whether any mechanism can be actually devised
which shall draw from the wind the power to cause a body wholly immersed in it
to go against the wind, the reader’s consideration is now first invited to the evidence
that there is no contradiction to the known laws of motion, and at any rate no theo-
retical impossibility in the conception of such a mechanism, if it is admitted that
the wind is not what it has been ordinarily taken to be, but what the following
observations show that it is.

What immediately follows is an account of evidence of the complex nature of
the “wind,” of its internal movements, of the resulting potentiality of this
internal work, and of attempts which the writer has made to determine quantita-
tively its amount by the use of special apparatus, recording the changes which go
on (so to speak) within the wind at very brief intervals. These results may, it is
hoped, be of interest to meteorologists, but they are given here with special refer-
ence to their important bearing on the future of what the writer has ventured to
call the science of Aérodromies.*

The observations which are first given were made in 1887 at Allegheny, and
are supplemented by others made at Washington in the present year.+

What has just been said about their possible importance will perhaps seem
justified, if it is remarked (in anticipation of what follows later) that the result of
the present discussion implies not only the theoretical, but the mechanical possi-
bility, that a heavy body, wholly immersed in the air and sustained by it, may,

* From aepod pouéw, to traverse the air; a@epodpos0S, an air-runner.

t It will be noticed that the fact of observation here is not so muchthe movement of cur-
rents, such as the writer has since learned was suggested by Lord Rayleigh so long ago as 1883,
still less of the movement of distinct currents at a considerable distance above the earth’s surface,
but of what must be rather called the effect of the irregularities and pulsations of any ordinary
wind within the immediate field of examination, however narrow.

See the instructive article by Lord Rayleigh in ature, April 5, 1883. Lord Rayleigh remarks
that continued soaring implies: “‘(1) that the course is not horizontal ; (2) that the wind is not
horizontal ; or (3) that the wind is not uniform.” “It is probable,” he says, “that the truth is
usually represented by (1) or (2) ; but the question I wish to raise is whether the cause suggested
by (3) may not sometimes come into operation,”

6 THE INTERNAL WORK OF THE WIND.

without the ordinary use of wind, or sail, or steam, and without the expenditure of
any power except such as may be derived from the ordinary winds, make an
aérial voyage in any direction, whose length is only limited by the occurrence of a
calm. A ship is able to go against a head-wind by the force of that wind, owing
to the fact that it is partly immersed in the water, which reacts on the keel, but it
is here asserted, that (contrary to usual opinion and in opposition to what at first
may seem the teachings of physical science) it is not impossible that a heavy and
nearly inert body, wholly immersed in the air, can be made to do this.

The observations on which the writer’s belief in this mechanical possibility
are founded, will now be given.

PART Ti
EXPERIMENTS WITH THE USE OF SPECIAL APPARATUS.

In the ordinary use of the anemometer, (let us suppose it to be a Robinson’s
anemometer, for illustration,) the registry is seldom taken as often as once a minute ;
thus, in the ordinary practice of the United States Weather Bureau, the registration
is made at the completion of the passage of each mile of wind. If there be very
rapid fluctuations of the wind, it is obviously desirable, in order to detect them, to
observe the instrument at very brief intervals, e g., at least every second, instead
of every minute or every hour, and it is equally obvious that in order to take up
and indicate the changes which occur in these brief intervals, the instrument
should have as little inertia as possible, its momentum tending to falsify the facts,
by rendering the record more uniform than would otherwise be the case.

In 1887 I made use of the only apparatus at command, an ordinary small
Robinson’s anemometer, having cups 3 inches (7.5 cm.) in diameter, the centre of
the cups being 63 inches (163 em.) from the centre of rotation. This was placed
at the top of a mast 53 feet (16.2 metres) in height, which was planted in the
grounds of the Allegheny Observatory, on the flat summit of a hill which rises
nearly 400 feet (122. metres) above the valley of the Ohio River. It was, accord-
ingly, in a situation exceptionally free from those irregularities of the wind
which are introduced by the presence of trees and of houses, or of inequalities of
surface.

Every twenty-fifth revolution of the cups, was registered by closing an electric
circuit, and the registry was made on the chronograph of the Observatory by a
suitable electric connection, and these chronograph sheets were measured, and the
results tabulated. A portion of the record obtained on July 16, 1887, is given on
Plate L, the abscisse representing time, and the ordinates wind velocities. The
observed points represent the wind’s velocities as computed from the intervals
between each successive electrical contact, as measured on the chronograph sheets,
and for convenience in following the succession of observed points they are here
joined by straight lines, though it is hardly necessary to remark that the change in
velocity is in fact, though quite sharp, yet not in general discontinuous, and the
straight lines here used for convenience do not imply that the rate of change of

velocity is uniform.

8 THE INTERNAL WORK OF THE WIND.

The wind velocities during this period of observation ranged from about 10 to

bo
o

5 miles an hour, and the frequency of measurement was every 7 to 17 seconds.
If, on the one hand, owing to the weight and inertia of the anemometer, this is far
from doing justice to the actual irregularities of the wind; on the other, it equally
shows that the wind was far from being a body of even approximate uniformity of

motion, and that, even when considered in quite small sections, the motion was

found to be irregular almost beyond conception,—certainly beyond anticipation ;
for this record is not selected to represent an extraordinary breeze, but the normal
movement of an ordinary one.

By an application of these facts, to be presented later, I then reached by these
experiments the conclusion that it was theoretically possible to cause a heavy body
wholly immersed in the wind to be driven in the opposite direction, ¢. g., to move
east while the wind was blowing west, without the use of any power other than
that which the wind itself furnished, and this even by the use of plane sur-
faces, and without taking advantage of the more advantageous properties of curved
ones.

This power, I further already believed myself warranted by these experiments
in saying, could be obtained by the movements of the air in the horizontal plane
alone, even without the utilization of currents having an upward trend. But I was
obliged to turn to other occupations, and did not resume these interesting observa-
tions until the year 1893.

Although the anemometer used at Allegheny served to illustrate the essential
fact of the rapid and continuous fluctuations of even the ordinary and comparatively
uniform wind, yet owing to the inertia of the arms and cups, which tended to
equalize the rate (the moment of inertia was approximately 40,000 gr. em.*), and to
the fact that the record was only made at every twenty-fifth revolution, the internal
changes in the horizontal component of the wind’s motion, thus representing its
potential work, were not adequately recorded.

In January, 1893, I resumed these observations at Washington with apparatus
with which I sought to remedy these defects, using as a station the roof of the
north Tower of the Smithsonian Institution building, the top of the parapet being
142 feet (43.3 metres) above the ground, and the anemometers, which were located
above the parapet, being 153 feet (46.7 metres) above the ground. I placed them in
charge of Mr. George E. Curtis, with instructions to take observations under the
conditions of light, moderate, and high winds. The apparatus used was, first, a
Weather Bureau Robinson anemometer of standard size, with aluminum cups.
Diameter to centre of cups 34 cm.; diameter of cups 10.16 cm.; weight of arms and
cups 241 grammes; approximate moment of inertia, 40,710 gr. em.

THE INTERNAL WORK OF THE WIND. 9

A second instrument was a very light anemometer, having paper cups, of
standard pattern and diameter, the weight of arms and cups being only 74
grammes, and its moment of inertia 8,604 gr. em.’

With this instrument, a number of observations were taken, when it was lost
by being blown away in a gale. It was succeeded in its use by one of my own
construction, which was considerably lighter. This was also blown away. I after.
ward employed one of the same size as the standard pattern, weighing 48 grammes,
having a moment of inertia of 11,940 gr. cm.’, and finally I constructed one of one
half the diameter of the standard pattern, employing cones instead of hemispheres,
weighing 5 grammes, and having a moment of inertia of but 300 gr. em.’

In the especially light instruments, the electric record was made at every half-
revolution, on an ordinary astronomical chronograph, placed upon the floor of the
Tower, connected with the anemometers by an electric circuit. Observations were
made on January 14, 1893, during a light wind having a velocity of from 9 to
17 miles an hour; on January 25 and 26, during a moderate wind having a
velocity of from 16 to 28 miles an hour; and on February 4 and 7, during a
moderate and high wind ranging from 14 to 36 miles an hour, Portions of these
observations are given on Plates II, III, and IV. A short portion of the record
obtained with the standard Weather Bureau anemometer during a high north-
west wind is given on Plate V.

A prominent feature presented by these diagrams is that the higher the abso-
lute velocity of the wind, the greater the relative fluctuations which occur in it.
In a high wind the air moves in a tumultuous mass, the velocity being at one
moment perhaps 40 miles an hour, then diminishing to an almost instantaneous
calm, and then resuming.*

The fact that an absolute local calm can momentarily occur during the prev-
alence of a high wind, was vividly impressed upon me during the observations of
February 4, when chancing to look up to the light anemometer, which was
revolving so rapidly that the cups were not separately distinguishable, I saw
them completely stop for an instant, and then resume their previous high speed of
rotation, the whole within the fraction of a second. This confirmed the suspicion
that the chronographic record, even of a specially light anemometer, but at most
imperfectly notes the sharpness of these internal changes. Since the measured
interval between two electric contacts is the datum for computing the velocity, an
instantaneous stoppage, such as I accidentally saw, will appear on the record
simply as a slowing of the wind, and such very significant facts as that just noted,
will be necessarily slurred over, even by the most sensitive apparatus of this kind.

* An example of a very rapid change may be seen on Plate IV., at 12.23 P.M.

10 THE INTERNAL WORK OF THE WIND.

However, the more frequent the contacts, the more nearly an exact record of
the fluctuations may be measured, and I have, as I have stated, provided that they
should be made at every half-revolution of the anemometer, that is, as a rule,
several times a second.*

I now invite the reader’s attention to the actual records of rapid changes that
take place in the wind’s velocity, selecting as an illustration the first 53 minutes of
the diagram plotted on Plate II.

The heavy line through points A, B, and C, represents the ordinary record
of the wind’s velocity as obtained from a standard Weather Bureau anemometer
during the observations recording the passage of two miles of wind. The velocity,
which was, at the beginning of the interval considered, nearly 23 miles an hour,
fell during the course of the first mile to a little over 20 miles an hour. This is
the ordinary anemometric record of the wind at such elevations as this (47 metres)
above the earth’s surface, where it is free from the immediate vicinity of disturb-
ing irregularities, and where it is popularly supposed to move with occasional
variation in direction, as the weather-cock indeed indicates, but with such nearly
uniform movement that its rate of advance is, during any such brief time as two or
three minutes, under ordinary circumstances, approximately uniform. This then
may be called the “wind,” that is, the conventional “ wind ” of treatises upon aéro-
dynamics, where its aspect as a practically continuous flow is alone considered.
When, however, we turn to the record made with the specially light anemometer,
at every second, of this same wind, we find an entirely different state of things.
The wind starting with the velocity of 28 miles an hour, at 12 hrs. 10 mins. 18
secs., rose within 10 seconds to a velocity of 33 miles an hour, and within 10
seconds more fell to its initial speed. It then rose within 30 seconds to a velocity
of 36 miles an hour, and so on, with alternate risings and fallings, at one time
actually stopping; and, as the reader may easily observe, passing through 18
notable maxima and as many notable minima, the average interval from a maximum
to a minimum being a little over 10 seconds, and the average change of velocity in
this time being about 10 miles an hour. In the lower left-hand corner of Plate IIT.

* Here we may note the error of the common assumption that the ordinary anemometer, how-
ever heavy, will, if frictionless, correctly measure the velocity of the wind, for the existence of “vis
inertia, ” it is now seen, is not indifferent, but plays a most important part where the velocity suffers
such great and frequent changes as we here see it does, and where the rate at which this inertia is
overcome, and this velocity changed, is plainly a function of the density of the fluid, which density
we also see reason to suppose, itself varies incessantly and with great rapidity. Though it is prob-
able that no form of barometer in use does justice to the degree of change of this density, owing to
this rapidity, we cannot, nevertheless, suppose it to exceed certain limits, and we may treat the
present records, made with an anemometer of such exceptional lightness, as being comparatively
unaffected by these changes in density, though they exist.

THE INTERNAL WORK OF THE WIND. 11

is given a conventional representation of these fluctuations, in which this average
period and amplitude is used as a type. The above are facts, the counterpart of
which may be noted by any one adopting the means the writer has employed. | It
is hardly necessary to observe, that almost innumerable minor maxima and minima
presented themselves, which the drawing cannot depict.

In order to insure clearness of perception, the reader will bear in mind that
the diagram does not represent the velocities which obtained coincidentally, along
the length of two miles of wind represented, nor the changes in velocity experi-
enced by a single moving particle during the given interval, but that it is a picture
of the velocities which were in this wind at the successive instants of its passing
the fixed anemometer, which velocities, indeed, were probably nearly the same for
a few seconds before and after registry, but which incessantly passed into, and
were replaced by others, in a continuous flow of change. But although the obser-
vations do not show the actual changes of velocity which any given particle
experiences in any assigned interval, these fluctuations cannot be materially
different in character from those which are observed at a fixed point, and are
shown in the diagram. It may perhaps still further aid us in fixing our ideas, to
consider two material particles as starting at the same time over this two-mile
course: the one moving with the uniform velocity of 22.6 miles an hour (33 feet per
second), which is the average velocity of this wind as observed for the interval
between 12 hrs. 10 mins. 18 secs., and 12 hrs. 15 mins. 45 sees, on February 4;
the other, during the same interval, having the continuously changing velocities
actually indicated by the light anemometer as shown on Plate III. Their positions
at any time may, if desired, be conveniently represented in a diagram, where the
abscissa of any point represents the elapsed time in seconds, and the ordinates
show the distance, in feet, of the material particle from the starting-point. The
path of the first particle will thus be represented by a straight line, while the path
of the second particle will be an irregularly curved line, at one. time above, and at
another time below, the mean straight line just described, but terminating in coinci-
dence with it at the end of the interval. If, now, all the particles in two miles of
wind were simultaneously accelerated and retarded in the same way as this second
particle, that is, if the wind were an inelastic fluid, and moved like a solid cylinder,
the velocities recorded by the anemometer would be identical with those that
obtained along the whole region specified. But the actual circumstances must evi-
dently be far different from this, since the air is an elastic and nearly perfect fluid,
subject to condensation and rarefaction. Hence the successive velocities of any given
particle (which are in reality the resultant of incessant changes in all directions),
must be conceived as evanescent, taking on something like the sequence recorded

12 THE INTERNAL WORK OF THE WIND.

by these curves, a very brief time before this air reached the anemometer, and
losing it as soon after.

It has not been my purpose in this paper to enter upon any inquiry as to the
cause of this non-homogeneity of the wind. The irregularities of the surface topog-
raphy (including buildings, and every other surface obstruction) are commonly
adduced as a sufficient explanation of the chief irregularities of the surface wind ;
yet I believe that, a considerable distance above the earth’s surface (¢. g. one mile),
the wind may not even be approximately homogeneous, nor have an even flow ; for
while, if we consider air as an absolutely clastic and frictionless fluid, any motion
impressed upon it would be preserved forever, and the actual irregularities of the
wind would be the results of changes made at any past time, however remote ; so
long as we admit that the wind, without being absolutely elastic and frictionless,
is nearly so, it seems to me that we may consider that the incessant alterations which
it here appears make the “wind,” are due to past impulses and changes which are
preserved in it, and which die away with very considerable slowness. If this be the
case, it is less difficult to see how even in the upper air, and at every altitude, we
might éxpect to find local variations, or pulsations, not unlike those which we
certainly observe at minor altitudes above the ground.*

*Tn this connection, reference may be made to the notable investigations of Helmholtz, on
Atmospheric Movements, Sttzungsberichte, Berlin, 1888-1889.

PART TE
APPLICATION.

Of these irregular movements of the wind, which take place up, down, and on
every side, and are accompanied of necessity by equally complex condensations and
expansions, it will be observed that only a small portion, namely, those which occur
in a narrow current whose direction is horizontal and sensibly linear, and whose
width is only the diameter of the anemometer, can be noted by the instruments I
have here described, and whose records alone are represented in the diagrams.
However complex the movement may appear as shown by the diagram, it is then
far less so than the reality, and it is probable, indeed, that anything like a fairly
complete graphical representation of the case is impossible.

I think that on considering these striking curves (Plates L, IT., III., IV., and
V.) we shall not find it difficult to admit, at least as an abstract conception, that
there is no necessary violation of the principle of the conservation of energy im-
plied in the admission thata body, wholly immersed in and moving with such a wind,
may derive from it a force which may be utilized in Uifting the body, in a way in
which a body immersed in the “wind” of our ordinary conception could not be
lifted, and if we admit that the body may be lifted, it follows obviously that it
may descend under the action of gravity from the elevated position, on a sloping
path, to some distance in a direction opposed to that of the wind which lifted it,
though it is not obvious what this distance is.

We may admit all this, because we now see (I repeat) that the apparent viola-
tion of law arises from a tacit assumption which we, in common with all others, may
have made, that the wind is an approximately homogeneously moving body, because
moving as a whole in one direction. It is, on the contrary, always, as we see here,
filled (even if we consider only movements in some one horizontal plane) with
amazingly complex motions, some of which, if not in direct opposition to the main
movement, are relatively so, that is, are slower, while others are faster than this
main movement, so that a portion is always opposed to it.

From this, then, we may now at least see that it is plainly within the capacity
of an intelligence like that suggested by Maxwell, and which Lord Kelvin has
called the “Sorting Demon,” to pick out from the internal motions those whose

13

14 THE INTERNAL WORK OF THE WIND.

direction is opposed to the main current, and to omit those which are not so, and
thus without the expenditure of energy to construct a foree which will act against
the main current itself.

But we may go materially further, and not only admit that it is not necessary
to invoke here, as Maxwell has done in the case of thermo-dynamics, a being having
a power and rapidity of action far above ours, but that, in actual fact, a being of a
lower order than ourselves, guided only by instinct, may so utilize these internal
motions.

We might not indeed have conceived this possible, were it not that nature has
already, to a large extent, exhibited it before our eyes in the soaring bird,* which
sustains itself endlessly in the air with nearly motionless wings, for without this
evidence of the possibility of action which now ceases to approach the inconceiv-
able, we are not likely, even if we admitted its theoretical possibility, to have thought
the mechanical solution of this problem possible. But although to show how this
physical miracle of nature is to be imitated, completely and in detail, may be found
to transcend any power of analysis, I hope to show, that this may be possible with-
out invoking the asserted power of “ Aspiration” relative to curved surfaces, or the
trend of upward currents, and even to indicate the probability that the mechanical
solution of this problem may not be beyond human skill.

To this conclusion we are invited by the following considerations, among others.

We will presently examine the means of utilizing this potentiality of internal
work, in order to cause an inert body, wholly unrestricted in its motion and wholly
immersed in the current, to rise; but first let us consider such a body (a plane)

* “When the condors ina flock are wheeling round and round any spot, their flight is beau-
tiful. Except when rising from the ground, I do not recollect ever having seen one of these birds
flap its wings. Near Lima, I watched several for nearly half an hour without once taking off
my eyes. They moved in large curves, sweeping in circles, descending and ascending without
once flapping. As they glided close over my head, I intently watched, from an oblique position,
the outlines of the separate and terminal feathers of the wings; and if there had been the least
vibratory movement these would have blended together, but they were seen distinct against the blue
sky. he head and neck were moved frequently and apparently with force, and it appeared as if
the extended wings formed the fulcrum on which the movements of the neck, body, and tail acted.
If the bird wished to descend, the wings for a moment collapsed ; and then when again expanded with
an altered inclination the momentum gained by the rapid descent, seemed to urge the bird upwards,
with the even and steady movement of a paper kite. In the case of any bird soaring, its motion must
be sufficiently rapid so that the action of the inclined surface of its body on the atmosphere may
counterbalance its gravity. The force to keep up the momentum of a body moving in a horizontal
plane in that fluid (in which there is so little friction) cannot be great, and this force is all that is
wanted, The movement of the neck and body of the condor, we must suppose, is sufficient for
this. However this may be, it is truly wonderful and beautiful to+see so great a bird, hour after
hour, without any apparent exertion, wheeling and gliding over mountain and river.”

Darwin’s Yournal of Various Countries Visited by H. M. S. Beagle, pp. 223, 224.

THE INTERNAL WCRK OF THE WIND. 15

whose movement is restricted in a horizontal direction, but which is free to rise be-
tween frictionless vertical guides. Let it be inclined upward at a small angle
toward a horizontal wind, so that only the vertical component of the pressure of
the wind on the plane will affect its motion. If the velocity of the wind be
sufficient, the vertical component of pressure will equal or exceed the weight
of the plane, and in the latter case the plane will rise indefinitely.

Thus, to take a concrete example, if the plane be a rectangle whose length
is six times its width, having an area of 2.3 square feet to the pound, and be
inclined at an angle of 7°, and if the wind have a velocity of 386 feet per second,
experiment shows that the upward pressure will exceed the weight of the plane,
and the plane will rise, if between vertical nearly frictionless guides, at an in-
creasing rate, until it has a velocity of 2.52 feet per second,* at which speed the
weight and upward pressure are in equilibrium. Hence, there are no unbalanced
forces acting, and the plane will have attained a state of uniform motion.

Fora wind that blows during 10 seconds, the plane will therefore rise about
25 feet. At the beginning of the motion, the inertia of the plane makes the rate of
rise less than the uniform rate, but at the end of 10 seconds, the inertia will cause the
plane to ascend a short distance after the wind has ceased, so that the deficit at the
beginning will be counterbalanced by the excess at the end of the assigned interval.

We have just been speaking of a material heavy plane permanently sustained
in vertical guides, which are essential to its continuous ascent ina uniform wind, but
such a plane will be lifted and sustained momentarily, even if there be no vertical
guides, or, in the case of a kite, even if there be no cord to retain it, the inertia of
the body supplying for a brief period the office of the guides or of the cord. If
suitably disposed, it will, as the writer has elsewhere shown, under the resistance to
a horizontal wind, imposed only by its inertia, commence to move, not in the diree-
tion of the wind, but nearly vertically. Presently, however, as we recognize, this
inertia must be overcome, and as the inclined plane takes up more and more the
motion of the wind, the lifting effect must grow less and less (that is to say, if the
wind be the approximately homogeneous current it is commonly treated as being),
and finally ceasing altogether, the plane must ultimately fall. If, however, a counter-
current is supposed to meet this inclined plane, before the effect of its inertia is
exhausted, and consequently before it ceases to rise, we have only to suppose the
plane to be rotated through 180° about a vertical axis, without any other call for
the expenditure of energy, to see that it will now be lifted still higher, owing to the

* See Experiments in Aérodynamics, by S. P. Langley. Smithsonian Contributions to
Knowledge, 1891.

16 THE INTERNAL WORK OF THE WIND.

fact that its inertia now reappears as an active factor. The annexed sketch (Fig.
1) shows a typical representation of what might be supposed to happen with a

Ss
-
—-
i
-—e—
oa
Fig.1.

model inclined plane freely suspended in the air, and endowed with the power of
rotating about a vertical axis so as to change the aspect of its constant inclination,
which need involve no (theoretical) expenditure of energy, even although the plane
possess inertia. We see that this plane would rise indefinitely by the action of the
wind in alternate directions.

The disposition of the wind which is here supposed to cause the plane to rise,
appears at first sight an impossible one, but we shall next make the important ob-
servation that it becomes virtually possible by a method which we shall now point
out, and which leads to a practicable one which we may actually employ.

‘A

Fig. 2.

Figure 2 shows the wind blowing in one constant direction, but alternately at
two widely varying velocities, or rather (in the extreme case supposed in illustra-

THE INTERNAL WORK OF THE WIND. 17
tion), wher? one of the velocities is negligibly small, and where successive pulsations
in the same directions are separated by intervals of calm.

A frequent alternation of velocities, united with constancy of absolute direc-
tion, has previously been shown here to be the ordinary condition of the wind’s
motion; but attention is now particularly called to the fact that while these un-
equal velocities may be in the same direction as regards the surface of the earth, yet
as regards the mean motion of the wind they are in opposite directions, and will
produce on a plane, whose inertia enables it to sustain a sensibly uniform motion
with the mean velocity of this variable wind, the same lifting effect as if these same
alternating winds were in absolutely opposed directions, provided that the (constant)
inclination of the plane alternates in its aspect to correspond with the changes in
the wind.

It may aid in clearness of conception, if we imagine a set of fixed co-ordinates X
Y Z passing through 0, and a set of movable co-ordinates x y z, moving with the
velocity and in the direction of the mean wind. If the moving body is referred to these
first only, itis evidently subject to pulsations which take place in the same directions
on the axis of X, but it must be also evident that if referred to the second or mova-
ble co-ordinates, these same pulsations may be, and are, in opposite directions. This,
then, is the case we have just considered, and if we suppose the plane to change
the aspect * of its (constant) inclination as the direction of the pulsations changes,
it is evident that there must be a gain in altitude with every pulsation, while the
plane advances horizontally with the velocity of the mean wind.

During the period of maximum wind velocity, when the wind is moving faster
than the plane, the rear edge of the latter must be elevated. During the period of
minimum velocity, when the plane, owing to its inertia is moving faster than the
wind, the front edge of the plane must be elevated. Thus the vertical component
of the wind pressure, as it strikes the oblique plane, tends, in both cases, to give it
a vertical upward thrust. So long as this thrust is in excess of the weight to be
lifted, the plane will rise. The rate of rise will be the greatest at the beginning of
each period, when the relative velocity is greatest, and will diminish as the resist-
ance produces “drift”; 7. ¢, diminishes relative velocity. The curved line O B in
the vignette represents a typical path of the plane under these conditions.

It follows from the diagram (Fig. 1.) that, other things being equal, the more
frequent the wind’s pulsations, the greater will be the rise of the plane; for since,
during each period of steady wind, the rate of rise diminishes, the more rapid the

*We do not for the moment consider how this change of aspect is to be mechanically effected ;
we only at present call attention to the fact that it involves, in theory, no expenditure of energy.

18 THE INTERNAL WORK OF THE WIND.

pulsations, the nearer the mean rate of rise will be to the initial rate. The requisite
frequency of pulsations is also related to the inertia of the plane, as the less the
inertia, the more frequent must be the pulsations in order that the plane shall not
lose its relative velocity.

It is obvious that there is a limit of weight which cannot be exceeded if the
body is to be sustained by any such fluctuations of velocity as can be actually ex-
perienced. Above this limit of weight, the body will sink. Below this limit, the
lighter the body is, the higher it will be carried, but with increasing variability of
speed. ‘That body, then, which has the greatest weight per unit of surface, will
soar with the greatest steadiness, if it soar at all, not on account of this weight, per
se, but because the weight is an index of its inertia.

The reader who will compare the results of experiments made with any artificial
flying models, like those of Penaud, with the weights of the soaring birds as given
in the tables by M. Mouillard, or other authentic sources, cannot fail to be struck
with the great weight in proportion to wing surface, which nature has given to the
soaring bird, compared with any which man has yet been able to imitate in his
models. This fact of the weight of the soaring bird in proportion to its area, has
been again and again noted, and it has been frequently remarked that without weight
the bird could not soar, by writers who felt that they could very safely make such
a paradoxical statement, in view of the evidence nature everywhere gave, that this
weight was indeed in some way necessary to rising. But these writers have not
shown, so far as I remember, how this necessity arises, and this is what I now
endeavor to point out.*

It has not here been shown what limit of weight is imposed to the power of an
ordinary wind to elevate and sustain, but it seems to me, and I hope that it may so
seem to the reader, that the evidence that there is some weight which the action of
the wind is sufficient to permanently sustain under these conditions in a free body,
has a demonstrative character, although no quantitative formula is offered at this
stage of the investigation. It is obvious that, if this weight is sustainable at any
height, gravity may be utilized to cause the body (which we suppose to be a
material plane) to descend on an inclined course, to some distance, even against
the wind.

I desire in this connection to remark that the preceding experiments and

* Tt is perhaps not superfluous to recall here that, according to the researches of Rankine, Froude,
and others, a body moulded in wave-line curves would, if frictionless, continue to move indefinitely
against an opposed wind in virtue of inertia and once acquired velocity, and also to recall how very
small the effect of fluid friction in the air has been shown to be (by the writer in a previous
investigation).

7,

THE INTERNAL WORK OF THE WIND. US)

deductions, showing that a material free plane,* possessing sufficient inertia, may in
theory rise indefinitely by the action of an ordinary wind, without the expenditure
of work from any internal source (as well as those statements which follow), when
these explanations are once made, have a character of obviousness, which is due to
the simplicity of the enunciation, but not, I think, to the familiarity of the explana-
tion ; for though attention is beginning to be paid by meteorologists to the rapidity
of these wind fluctuations, I am not aware that their effects have been so exhibited,
or especially that they have been presented in this connection, or that the conclu-
sions which follow have been drawn from them.

We have here seen, then, how pulsations of sufficient amplitude and frequency,
of the kind which present themselves in nature, may, in theory, furnish energy not
only sufficient to sustain, but actually to elevate, a heavy body moving in and
with the wind at its mean rate.

It is easy to now pass to the practical case which has been already referred to,
and which is exemplified in nature; namely, that in which the body (e. g. the bird
soaring on rigid wings, but having power to change its inclination) uses the eleva-
tion thus gained to move against the wind without expending any sensible amount
of its own energy. Here the upward motion is designedly arrested at any conven-
ient stage, ¢ g. at each alternate pulsation of the wind, and the height attained is
utilized so that the reaction of gravity may carry the body by its descent in a curvi-
linear path (if necessary) against the wind. It has just been pointed out that if
some height has been attained, the theoretical possibility of some advance against
the wind in so falling hardly needs demonstration, though it may not unnaturally
be supposed that the relative advance so gained must be insignificant, compared
with the distance travelled by the mean wind while the body was being elevated,
so that on the whole the body is carried by the wind farther than it advances
against it.

This, however, probably need not be in fact the case, there being, as it appears
to me, from experiment and from deduction, every reason to believe that under
suitable conditions, the advance may be greater than the recession, or that the body,
falling under the action of gravity along a suitable path, may return against the
wind not only from Z to O, the point of departure, but farther, as is here shown.

I repeat, however, that I am not at the moment undertaking to demonstrate

* T use the word “plane,” but include in the statement all suitable modifications of a curved
surface.

I desire to recall attention to the paragraph in Zxperiments in Aérodynamics in which I
caution the reader against supposing that by investigating plane surfaces I imply that they are the

best form of surface for flight ; and I repeat here that, as a matter of fact, I do not believe them to
be so. I have selected the plane simply as the best form for preliminary experiment.

20 THE INTERNAL WORK OF THE WIND.

how the action is mechanically realizable in actual practice, but only that it is pos-
sible. It is for this purpose, and to understand more exactly that it can be effected,
not only by the process indicated in the second illustration (Fig. 2), but by another
and probably more usual one (and nature has still others at command), that I have
considered another treatment of the same conditions of wind-pulsations always
moving in the same horizontal direction, but for brief periods interrupted by equal
intervals of calm. In this third illustration (Fig. 3) we suppose the body to use
the height gained by each pulsation to enable it to descend after each such pulsa-

tion, and advance against the direction of the wind.

D

Fic. 3.

The portion A B of the curve represents the path of the plane surface from a
state of rest at A, where it has a small upward inclination toward the wind. If a
horizontal wind blow upon it in the direction of the arrow, the first movement of
the plane will not be in the direction of the wind, but as is abundantly demon-
strated by the writer in Experiments in Aérodynamics, it will rise in nearly ver-
tical direction, if the angle be small. The wind, continuing to blow in the same
direction, at the end of a certain time, the plane, which has risen (owing to its iner-
tia and in spite of its weight) to the successive positions shown, is taking up more
and more of the horizontal velocity of the wind, and consequently opposing less
resistance to it, and therefore moving more and more laterally, and rising less and
less, at every successive instant.

If the wind continued indefinitely, the plane would ultimately take up its
velocity, and finally, of course, fall, when this inertia ceased to oppose resistance to
the wind’s advance. I have supposed, however, the wind-pulsation to cease at the
end of a certain brief period, and, to fix our ideas, let us suppose this period to be
five seconds. At this moment the period of calm begins, and now let the plane,
which is supposed to have reached the point B, change its inclination about a hori-
zontal axis to that shown in the diagram, falling at first nearly vertically, with its
edge on the line of its descent so as to acquire speed, and this speed, acquired by

constantly changing its angle, glide down the curve B C, so that the plane shall be

THE INTERNAL WORK OF THE WIND. 21

tangential to it at every point of its descending advance. At the end of five
seconds of calm it has reached the position C, near the lowest point of its descent,
which there is no contradiction to known mechanical laws in supposing may be
higher than A, and which, in fact, according to the most accurate data the writer
can gather, 7s higher in the case of the above period, and in the case of such an
actual plane as has been experimented upon by him.

Now, having reached C, at the end of the five seconds’ calm, if the wind blow
in the same direction and velocity as before, it will again elevate the plane, on the
latter’s presenting the proper angle, but this time under more favorable circum-
stances, for, at this time, the plane is already in motion in a direction opposed to
that of the wind, and is already higher than it was in its original position A. Its
course, therefore, will be nearly that along the curve C D, during all which time it
maintains the original angle a, or one very slightly less. Arrived at D, and at the
instant when the calm begins, it falls, with varying inclination, to the lowest posi-
tion E (which may be higher than C), which it attains at the end of the five seconds
of calm, then rises again (still nearly at the angle a) to a higher position, and so
on; the alternations of directions of motion, at the end of each pulsation, growing
less and less sharp, and the path finally taking the character of a sinuous curve.
We have here assumed that the plane goes against the wind and rises at the same
time, in order to illustrate that this is possible, though either alternative may
be employed, and the plane, in theory at least, may maintain on the whole a
rapid and nearly horizontal, or a slow and nearly vertical course, or anything
between. *

It is not meant, either, that the alternations which would be observed in
nature are as sharp as those here represented, which are intentionally exaggerated ;
while in all which has just preceded, by an equally intentional exaggeration of the
normal action, the wind-pulsations have been supposed to alternate with absolute
calm. This being understood, it is scarcely necessary to point out that if the calm
is not absolute, but if there are simply frequent successive winds or pulsations of
wind of considerably differing velocity (such as the anemometer observations show,
are realized in nature), that the same general effect will obtain, though we are not

* See the very interesting account (4éronautical Annual, No. 2, p. 66) by Mr. Chanute of the
successive steps by which sea-gulls were actually observed to get in motion without flapping.
The above @ priori reasoning reads almost like a description of Mr. Chanute’s subsequent ob-
servation.

22 THE INTERNAL WORK OF THE WIND.

entitled to assume from any demonstration thus far given that the total advance
will be necessarily greater than that of the whole distance the mean wind has
travelled. It may also be observed that the actual actions of the soaring bird may
be, and doubtless are, more complex in detail than those of this diagram, while yet
in their entirety depending on the principles it sets forth.

The theoretical possibility at least will now, it is hoped, be granted, not only
of the body’s rising indefinitely, or of its descending in the interval of calm to a
higher level C, than it rose from at A, but of its advancing against the calm
or light wind through a distance B C, greater than that of A B, and so on. The
writer, however, repeats that he has reason to suppose from the data obtained by
him, that this is not only a theoretical possibility but a mechanical probability
under the conditions stated, although he does not here offer a quantitative demon-
stration of the fact, other than by pointing to the movements of the soaring bird
and inviting their reconsideration in the light of the preceding statements.

The bird, by some tactile sensibility to the pressure and direction of the air,
is able, in nautical phrase, to “see the wind,” * and to time its movements, so that
without any reference to its height from the ground, it reaches the lowest portion
of its descent near the end of the more rapid wind pulsation ; but the writer be-
lieves that to cause these adaptive changes in an otherwise inert body, with what
might be almost called instinctive readiness and rapidity, does not really demand
intelligence or even instinct, but that the future aérodrome may be furnished with
a substitute for instinct, in what may perhaps allowably be called a mechanical -
brain, which yet need not, in his opinion, be intricate in its character. His reasons
for this statement, which is not made lightly, must, however, be reserved for
another time.

It is hardly necessary to point out that the nearly inert body in question may
also be a human body, guided both by instinet and intelligence, and that there may
thus be a sense in which human flight may be possible, although flight depending
wholly upon the action of human muscles be forever impossible.

Let me resume the leading points of the present memoir in the statement that
it has been shown :

(1) That the wind is not even an approximately uniform moving mass of air,
but consists of a succession of very brief pulsations of varying amplitude, and that,
relatively to the mean movement of the wind, these are of varying direction.

(2) That it is pointed ont that hence there is a potentiality of “internal work”

in the wind, and probably of a very great amount.

* Mouillard.

THE INTERNAL WORK OF THE WIND. 23

(8) That it involves no contradiction of known principles to declare that an
inclined plane or suitably curved surface, heavier than the air, freely immersed in,
and moving with the velocity of the mean wind, can, if the wind pulsations here
described are of sufficient amplitude and frequency, be sustained or even raised
indefinitely without expenditure of internal energy, other than that which is in-
volved in changing the aspect of its inclination at each pulsation.

(4) That since (A) such a surface, having also power to change its inclina-
tion, must gain energy through falling during the slower, and expend energy by
rising during the higher, velocities; and that (B) since it has been shown that
there is no contradiction of known mechanical laws in assuming that the surface
may be sustained or may continue to rise indefinitely, the mechanical possibility of
some advance against the direction of the wind follows immediately from this
capacity of rising. It is further seen that it is at least possible that this advance
against the wind may not only be attained relatively to the position of a body
moving with the speed of the mean wind, but absolutely, and with reference to a
fixed point in space.

(5) Ladd to the preceding results, which have been established here quali-
tatively, an expression of my personal opinion that they are realizable in practice.

Finally, these observations and deductions have, it seems to me, an important
practical application not only as regards a living creature like the soaring bird, but
still more, as regards a mechanically constructed body, whose specific gravity may
probably be many hundred or even many thousand times that of the atmosphere.
We may suppose such a body to be supplied with fuel and engines, which would
be indispensable to sustain it in a calm, and yet which we now see might be ordi-
narily left entirely inactive, so that the body could supposably remain in the air,
and even maintain its motion in any direction, without expending its energy,
except as regards the act of changing the inclination or aspect which it presents to
the wind while the wind blew.

The final application of these principles to the art of aérodromics seems then
to be that, while it is not likely that the perfected aérodrome will ever be able to
dispense altogether with the ability to rely at intervals on some internal source of
power, it will not be indispensable that this aérodrome of the future shall, in order
to go any distance—even to circumnavigate the globe without alighting,—need to
carry a weight of fuel which would enable it to perform this journey under con-
ditions analogous to those of a steamship, but that the fuel and weight need only

be such as to enable it to take care of itself in exceptional moments of calm.

Wasuineton, D. C.: August, 1893.

NOTE FROM THE FRENCH EDITION OF 1893.*

I have already drawn the reader’s attention to the fact that the accompanying
figures only show a small part of the virtual work of the wind. It will be under-
stood that a diagram like that in our text, intended only to show the path of a body
in one given trajectory, cannot represent all the conditions of Nature, which are at
once much more favorable and much more complex, since I have here exhibited
out of many conditions one only, selected for the single reason that it is best fitted
to elucidate the fundamental idea of this treatise.

So, too, I have spoken of a “plane” to aid my explanation, without meaning
that this form is actually best for flight, and without supposing that what has pre-
ceded about a perfected aerodrome could be misunderstood to mean that I would
actually employ only planes in such a machine, or employ them only under a con-
dition (that of a rectilinear horizontal wind) used here merely to simplify the
enunciation of a problem. On the contrary I believe the future xrodrome will
utilize not only the particular pulsation of the wind described here, but also its
ascending, lateral, and whirling motions.

* “Te Travail Intérieur du Vent.” Revue del Aéronautique, 1893.

APPENDIX.”

SOLUTION OF A SPECIAL CASE OF THE GENERAL PROBLEM.
By Ren DE SAUSSURE.

In this solution which has been selected from a number, independently ob-
tained, and relating to special cases, integration has been carried out between the
vertical tangent at the right of Figure 3 and the point D, as this interval bears
on the most important feature of the demonstration, that is: the proof that the
aéroplane can lift itself without expending a perceptible amount of energy while ©
making progress against the wind.

\

PROBLEM,

An aéroplane of mass m és projected into the air with an initial velocity Vi, at
an angle b with the horizontal. Find the velocity of the aéroplane at a given instant
and the equation of the trajectory described by its center of gravity.

(It is to be noted that as the velocity V is the velocity of the aéroplane
irrespective of the velocity of the wind, the problem is the same whether the
atmosphere is in motion or not, providing the codrdinate axes move with the air
currents. )

The proposed solution does not lead to an equation for the trajectory in & and
y, but it gives the value of y in terms of the angle £, the angle which the tangent
to the trajectory makes with the 2 axis, and permits it to be demonstrated that
within the limits between which that angle is supposed to vary, the aéroplane can,
under certain conditions, make progress against the wind. To prove this is the
aim of this paper.

The exact value of z in terms of f is not given here, although it is possible

to obtain it by a long series of calculations. It is simpler to use an approximate

* Translated from “Le Travail Intérieur du Vent,” par M. 8S. P. Langley, Revue de v Aégro-
nautique Theorique et Appliquée, pp. 58-68, Paris, 1893.
2
25

26 THE INTERNAL WORK OF THE WIND.

value, as the variable @ is not one of the unknowns important in reaching the
desired result.

In order that the trajectory described by the aeroplane may be definite, the
law of variation for the angle a between the aéroplane and the tangent of the
trajectory must be stated, for it is really by varying this angle at will that a bird
changes its course in the air.

To realize the most favorable conditions, this angle should be diminished as
the velocity increases, for instance it can be made to vary inversely as the square
of the velocity; this voluntary change of orientation can be accomplished, more-
over, without a perceptible expense of energy.

horizontal

Mg

Fie. 4.

It is probable that this law of variation which we have attributed to the
angle a is not that which offers the most favorable conditions for flight, but if our
object can be attained in this special case, the proof will hold @ fortéort under all
more favorable circumstances.

Suppose R is the resistance of the air pressing normally on the aeroplane at
its center of gravity, p the radius of curvature of the trajectory, and ¢ the time
(Fig. 4). The equations for the movement of the center of gravity are:

(av Ri

= an < sin &
| at > Pens m
4 yi

[ A — 9 cos f —= cos a

Furthermore : F = oe , the minus sign indicating that the angle 6 decreases
as the are s increases.

The resistance of the air R = ° V* f(@); 6 being the density of the air, A
the surface of the aeroplane, and f(@) a function of the angle a, experimentally

determined. As the angle a varies inversely as the square of the velocity, we

'
|
|
|

THE INTERNAL WORK OF ‘THE WIND. Did,

have a= wo e being a constant which can be so chosen that the angle a may haye
any desired value.

We will assign such a value to this constant that the angle a may always be
small, making it possible to neglect all powers of a greater than unity and to
assume (since /(@) should disappear when a=0) that :

sin @ = « cosiai— 1 f(@) = ha
h being a constant derived from experimental results.

Substituting these values in the equations for the movement of the center of

gravity, we have:

dV iN) : bf
f w= =—gsin f — — V*ha®
v2 dp 6A
Vee Se Va COs Gee oS
[ D> V3? a, = 9 COs p mg ¥ ha

. 6 c E 6 , i" <Q Sis 0 OA =
Replacing a by its value ,; , and calling for the sake of simplification er he=K,

we have finally:

( Vav : _¢

} ds =~ gsm h—Kya (1)
a)

| igs = 9 ee A +E 2)

1. Calculation of the velocity—To determine the velocity in terms of the an-
gle nsidering # as an independent variable, we divide each side of equation (1)
by the corresponding side of equation (2), which gives, after the denominators
have been eliminated :
V(g cos 6 — K)dV — V°g sin BdB = Ked &
a linear differential equation in V* whose integral factor is 2 (g cos 6 —K).
Multiplying the two sides of the preceding equation by this factor we get
2V (g cos 6 — K)*dV — 2V° (g cos 6 — K) g sin df = 2Ke (g cos 6 — K) df
each side of which is an exact differential ; from this we get by integrating :
V? (g cos 6 — K)? = 2Ke (g sin 6 — Kf) -+ Ce
the constant C being determined by the initial conditions of the movement. Sub-
stituting V, for V and 4 for 6 we obtain
V,? (g cos b — K)? = 2Ke (g sin b — Kb) + Ce
and by subtracting this equation from the preceding:
V?(g cos 8 — K)? = V,? (g cos b — K)? + 2Ke (g sin 6 — g sin b — Kf + Kb)
whence

+ i ——— — ‘
v= SS l ‘V ,¢ (g cos b —K)? + 2Ke (g sin 6 — g sin b — Kf + Kb) (3)

the value of VY in terms of /.

28 THE INTERNAL WORK OF TIE WIND.

2. Calculation of the ordinate y in terms of the angle 8.—Equation (1) can
be written:

Ke
VdV= — gsin fds — + ds

2

= substituting these

, ° ds _
= dy, and irc *quatlo PA ae
But sin 6ds = dy, and from equation (2), 7 Pry er a

the preceding equation becomes:

Kedf

Vay = gay + g cos B — ike

whence by integration :

oy aes vie ae ee re
Ni ‘ geos B — K

Here we have to consider three possible cases: where K is greater than, equal

to, or less than g.
= dp 1 K cos 6B — 9g
When Kk => YJ; i cos p — co VK? = = -@ arc sin ie SS)
In this case:
Ke : K cos 6 — g
es, AVS ——————————— eS le
2gy =— V?+2 Ve 9 are sin ¢ San= 2) +C
Since, considering the starting point of the aéroplane as the origin, the initial
conditions are: y¥ = 0, V =V,, 6 = 4, the constant C is obtained from the equation:

Kena K cos b —9
0=—V,;?+27,— eo ; are sin g cos b —K + Ce

We have then, substituting this value for C:

r ——_ [ are sin K cos 6 —g — are sin K cos b == (4)
NU SP g cos B —K g cosb —K

an equation which gives the vaiue of the ordinate y in terms of the angle £, the

2Qgy = V2 — V?

velocity V being already known.

When K = g,

dp =a dp = dp 1 B
gosB—K™~ g 1—(colp a 2 sin? 2 Foss

and therefore:

2gy = — V? + 2c cotang B + Ce

From initial conditions :
0 = — V,? -+ 2e¢ cotang 9 -+ Ce

whence by substitution :

2oy = V,? — V? + 2e (cotans B. -— cotang °) (5)

THE INTERNAL WORK OF THE WIND. 29

Finally, when K<g, the integral

J ee | Vena — cos AF
g cos BP — K p= ko

g cos 6 —K

We have then, in this case :

Ke [pa ama ve =O ra = 1
Diy = NP ES a ys [| AA K? sin 6 — K cos 6 + 9 Ce
ay eae ( eae +

the constant C coming from the equation :

Vg? Sa

0=-Vi+2

Log ws {pee SO AUS ari

g cos b —K ) +c

Substituting this value for C we obtain :

2oy = V,2— V2 + pa SS toe( V7? —K’ sin B—K cos 6 +g 9. C08 o— z) 6)

Vg — &? Vg? — K? sinb—Kcosb +g g cosf —K

One of these equations (4), (5), or (6), will give the value of y in terms
of g, but in each numerical example we must choose the equation which corre-
sponds to the ratio of K to g in that example.

It is well to note that the formula (6) which gives y when K< g can be put
into a form much more convenient for numerical calculation. This is effected by

calling . = cos ¢, as K < g in this case ; we get in this way :

Vip
1—— =sin@p

whence
2
ee ie p sin 6 — cos pcos B+ i
= 1 — cos (g + £#)
are Plata
== 2
and :
K a} =
g ~ 008 B = cos p — cos 6 = oem sin 2—F

Substituting these values in (6) and reducing, the equation becomes :

sin cee sin PL B

Ke
2oy = Vo? — V2 + 2 ———— log f —__ *
Ve — sine — B sin das
: ° : K cos P@
which can be written, since = —=——— = © ® = cotang 9:
d Vg—-K sing

: + 8
2gy = V,? — V? + 2c cotang p (tox sin 2°

ie —O b
— Log sin kde + Log sin —— — Log sin 2 28 )

In this form, equation (6) is eminently well suited for numerical calculation ;

30 THE INTERNAL WORK OF THE WIND.

it is only necessary to be careful to change the Naperian logarithms of the formula
into common logarithms.
3. Calculation of the abscissa x in terms of the angle 6.—Equation (2) can

be written
Fie Vedp
K —gcosf

: 7 5 es iidst . . . Enid A

and as ds = 7, we get after substituting and integrating :
B

V? cos fdf

K—gcosf
b

8
II

Such is the expression for #@ in terms of £. We assume, however, that V*
is to be replaced by its value in terms of # derived from equation (3). The com-
plete calculation of this integral is probably possible; it would be a very long
operation in any case, however, and as the unknown ~ is of little interest in the
result which we are working for, it is better to de satisfied with an approximate
value. This can easily be obtained, as the equation enables us to calculate the
velocity V corresponding to any value of angle 6 and consequently to determine

the curve:

V? cos £
K — g cos

The area of this curve relative to the axis of # is evidently a, since

B
x =) zd fi
b

4. Calculation of the time t in terms of £.—Equation (2) can be also written »

om ;
NV qt & — 90088

whence:

2

p
a Vdp - a
oo K — g cos f
b =:

The same remark that applies to 7 also applies to ¢, which can be obtained
more rapidly and with as close an approximation as desired by calculating the area

of the curve :
V
K—gcos fp

NUMERICAL EXAMPLE.

The purpose of this example is to show by means of given numerical quan
tities that an aéroplane can both rise and make progress against the wind, provided
that the velocity of the wind is variable.

THE INTERNAL WORK OF THE WIND. 3

For the sake of greater simplicity, and to work under the same conditions that
prevailed in Figure 4, let us assume that the air is alternately at rest and in
motion, each for a definite period of time, the velocity of the air while in motion
being constant. In other words, instead of assuming that the velocity of the air
varies continuously in obedience to a certain law we suppose that it jumps ab-
ruptly from zero to a finite value (to 12 meters per second for example), sustains
this speed for a certain period, and drops again abruptly to zero, the calm prevail-
ing for some seconds only to give place to a new puff, and so on.

If we suppose an aéroplane to be set free in a perfectly calm atmosphere, it
may happen that after having fallen a certain distance the aéroplane can reascend
on account of the increase of the resistance of the air with its velocity, but even
under the most favorable conditions, if its initial velocity is zero, it can never
regain the level from which it started.

In order to understand better the effect of successive puffs of wind on the
ascension of the aéroplane, it would be well to find out first to just what level the
aéroplane would ascend in a calm atmosphere.

Given quantities (see the text referring to Fig. 3):

Surface of the aéroplane : A = 1 square meter
Weight of the aéroplane : mg = 2 kilograms
Density of the air : 6 = 1.295
These quantities are chosen to correspond to those of the example previously
mentioned in this memoir, and not because they give the best results.
The angle @ should remain small, so we will assign as its limits 0 and 7°.
From the data of previous experiments on this subject,’ we find that the con-
stant 2 should be taken as 3.322 to represent conveniently the function 7 (@) be-
tween 0 and 7°. We have then, between these limits f(a) = 3.822 a.
In the equation a = on the constant ¢ should be selected so that the angle a
never exceeds 7°. We see that this condition is fulfilled if “is taken as 7.808.
We can now calculate out the expression K = _ and find that K = 16.769.
The initial velocity of the aéroplane is zero ; therefore, since a = vr the angle
a is infinite at the point of departure, although we have seen that the formule do
not apply when a is greater than 7°.
To remove this difficulty, however, it is only necessary to assume that the

aéroplane, remaining in a vertical position, falls by reason of its weight until it

1 Bexperiments in Aérodynamics. §. P. Langley. “Smithsonian Contributions to Know-
ledge,” vol. xxvii. 1891. We have chosen here the curye which represents the function 7 (@)
derived for an aéroplane whose breadth is six times its length, and whose motion is in

the direction of its short dimension.

32 THE INTERNAL WORK OF THE WIND.

gains a finite velocity. In such a position, the air offers no resistance to its motion
and it falls in a straight line. When the velocity acquired is sufficiently great the
hand that guides the aéroplane can vary its angle of inclination so as to satisfy
both the condition a< 7° and the equation a = .. The aéroplane then follows a
trajectory which can be determined by the equations given above. This trajectory
inclines upward, until at a certain point B’ the tangent is vertical. If now the
aéroplane, always under the control of the guiding hand,! is brought back to a ver-
tical position, the air offers no more resistance since the edge of the aéroplane is
presented. The aéroplane therefore ascends in a straight line. As the velocity at
B’ is already known, the maximum altitude that the aéroplane can reach in a calm
atmosphere can easily be calculated.
To sum up, the trajectory is made up of three parts (Fig. 5) :
from A to A’ the aéroplane falls in a straight line and a = 0;
from A’ to B’ the aéroplane follows the curve A’CB’ and a = ye
from B’ to B the aéroplane rises in a straight line and a = 0.
The problem is now to find the position of B with reference to A.
1. From A to A’ the aéroplane is propelled entirely by its weight; we have

therefore ae = g, in which V= gt and S = sgt *. By eliminating ¢ we have also
= = If we assume that the aéroplane falls in a straight line until it acquires

a velocity of 10 meters per second, we find that AA’ = 5.097465 m., the velocity
at A = 0, and the velocity at A’ = 10 meters per second.

2. From A’ to B’ the trajectory is determined from the equations previously
established, by introducing in them the conditions actually prevailing at the begin-
ning of the curve A’B’; these are V, = 10, b= — =, and consequently cos b= 0
and sin 6= 1.

To find the velocity at C, the lowest point on the curve, let 6= 0 in equation
(8); this gives, after numerical values have been substituted for all the constants,
Vc = 22.1607 m.

In the same way we find the velocity at B’, in this case calling 6 = which
gives Vp = 8.31924 m.

It has been remarked above that by taking ¢ as 7.808, the angle a will never
exceed 7 degrees ; in reality the maximum value of @ corresponds to the minimum

e ___7.808

of V, 8.819 m., and can be obtained from the formula a = y= sin? which gives

a result of about 6° 30’ for a, justifying the value arbitrarily assigned to c.

1 The changing of the orientation of the aéroplane necessitates the expenditure of a certain
amount of energy which is not taken account of here as it is very small.

THE INTERNAL WORK OF THE WIND. 33

Since K> g in the numerical example, the ordinate y is obtained from formula
(4) ; to find the ordinate at the point C we substitute 22.1607 for V and 0 for d in
this formula and get: y, = —22.0908 m.

From the same formula, by making V= 8.319 and = we get for the
ordinate of the point B’: y, = — 2.74013 m., A being taken as the origin for
these values.

3. From B’ to B the aéroplane is carried by its weight, which also retards its

ascent ; for this stretch we have therefore: “Y — — g and hence V = Vy,— gt and

Cte
S= Vit — = gt* |
At the point B, V =.0, and therefore gt = Vy. Substituting the value for ¢
from this equation in the equation for S we find that :

1 (8,319)?
BB =S=— — = i S Ee = 3.52794 m.

Correlating all the results thus far obtained, we have for the different vertical
distances traversed :

DESCENT ASCENT
From A to A’ 5.097465 m. From C to B’ 19.35067 m.
From A’ to C 22.0908 m. From B’ to B 3.52794 m.
Total 27.188265 m. Total 22.87861 m.

Thus the finishing point B is about 4.3 meters below the starting point A.

A

AV
A’

Direction of the Wind

Fia. 5. Fig. 6. Fig. 7.

(We have not yet calculated the abscissa of the point B as it is not of great
importance here. The time required by the aéroplane, however, in going from the
point A to the point B is found by the method of approximation previously men-
tioned to be about five seconds.)

If we suppose now that an aéroplane falls into a calm atmosphere under the
same conditions as in the preceding case, it will describe the same trajectory and
we wll have as before:

Vi— 0 Va=10 Vc =22.1067

Vertical distance from A to A’: 5.097465 m.
Vertical distance from A’ to C: 22.0908 m.

54 THE INTERNAL WORK OF THE WIND.

If a puff of wind, however, strikes the aéroplane when it has reached the point
C the second part of the trajectory will evidently be modified ; the problem is now
_to find to what height the aéroplane can ascend under these changed conditions,
the velocity of the wind being twelve meters per second for example.

We have seen that the same equations are applicable when the air is in
motion, provided that the codrdinate axes follow the displacement, for in such
a case the air is at rest in reference to the codrdinate axes. The trajectory ob-
tained under these conditions will not be the trajectory relative to the earth, but
that relative to the moving air. This offers no difficulties, however, as the diree-
tion of the wind is horizontal and therefore only the abscissee are changed when
we pass from the apparent trajectory to the actual one or vice versa.

In this case, as in the preceding, it is necessary to find the position of the
point where the tangent is vertical (Hig. 6).

Let CE be the trajectory relative to the moving air, and C D’ the trajectory
with reference to the earth. To find the ordinate of the point D’ where the tan-
gent is vertical it is only necessary to know that of the corresponding point E on
the other trajectory. The velocity at C relative to the earth has been found to be
22.1607 m.

This velocity, however, corresponds to the curve CD’; the velocity at C on
the curve CE, that is to say, the velocity at C of the aéroplane compared to the
air, is equal to 22.1607 + 12., or 34.1607 m.

In general, if we consider two points m and v situated at the same altitude,
the horizontal component of the velocity at m is equal to the horizontal component
of the velocity at plus the velocity of the wind. As this horizontal component
is zero at D’, that at E should be equal to the velocity of the wind. Thus,
to define the position of the point E on the curve CE we have the condition
Wicosye — 12,

Working tentatively with equation (3) we find, after having substituted in it
the initial conditions V, = 34.1607 and 6=0 (C being now considered as the
origin), that when 6= 55° 1’, V,= 20.9311 m. and consequently: V cos 6=
12.0006 m.!

Knowing the velocity at E, formula (4) gives us the ordinate of this point ;

we find in this way that: y, = 35.594 m.
This ordinate is also that of the point D’.

1'These values were cbtained by giving ¢ the same value as before : ¢=7.808. In reality, be-

tween A’ and K, that is to say in the interval where this value of ¢ was used, the minimum
Pee , ; : c 7.808
velocity is at A’, where V=10; therefore the maximum value for a = >> = “007 = 4° 30!

approximately, Thus in no case does the angle a reach 7 degrees,

THE INTERNAL WORK OF THE WIND. 5

or

Let us now suppose that the wind ceases when the aéroplane reaches the point
D’ (Fig. 7). The aéroplane will then find itself in a calm atmosphere and possessed
of a vertical velocity equal to: V,sin 6 = 20.9311 xX sin (55° 1’) = 17.1493 m.

If the aGroplane is now oriented in a vertical direction so as to eliminate air
resistance, this velocity of 17.1493 m. will enable it to cover in its ascent a space
DD’ = 14.9916 m. We have, therefore, for the different vertical distances
traversed:

DESCENT ASCENT
From A to A’ 5.097465 m. From C to D’ 35.594 m.
From A’ to C 22.0908 mm. From D' to D 14.9916 m.
Total 27.188265 m. Total 50.5856 m.

Thus the finishing point D is found to be about 23.40 meters above the start-
ing point A; furthermore, although we have not calculated a, it is certain that the
aéroplane has made progress against the wind, since the point D’ is to the left of
C which is itself to the left of the starting point A. In reality, from C to E the
horizontal component of the velocity is greater than the velocity of the wind; the
aéroplane therefore gains the distance from C to D’ with reference to the earth
since, as we have seen, the velocity of the aéroplane relative to the earth is equal
to the velocity relative to the air minus the velocity of the wind.

Finally, since its velocity at D is zero, the aéroplane is again in the same _posi-
tion as at the start; it can therefore repeat the same maneuvers and proceed
indefinitely by a series of bounds, provided of course, that the puffs of wind
succeed each other in regular order.

eee ea pee eo Cee ey eee oe wh One es On NA ws) 47 |. F >) -_=, a

*Inoy Jad sayIUI UI SaTzIDOTAA PULA, = S2}VUIPIO
‘OWI, = wssiosqy

"suoINfOAsT Sz K19A9 DulIa}stHa1 I9JaWOWsUL UOSUIqOY v YM AIO}vAIASqG AuaysalTy oy) 4v ‘Aggr ‘or Atn{ papsooar SOTIOOTAA PUTAA

mor ul woe ul wO2 yl wOl yl uO yl u0S yO wor yO

IT aLvid

18

16

Wind, S.S.E.; Weather, cloudy. R R Rh

PLATE II.

14

42

a I b
106 : \ J aaa
34m \em. 357 ag{™ am 38m 39 40™ 41™ 42m
18 E — : _ es — =
16 : - 4 {_

l4 — - :
12 I \ P M |
10 Y y a! . |
h4e™ PM 43™ \/ 44™ 45™ 46” 4a7™ 4gm 49m 50™
18 = —

pe

12 \ H
4
10 | \
8 — i: 2 ! H == ay —s ie ;
1"So™Pm Sie 52m 53™ 54m som s6™ 57™ ben.

Wind velocities recorded January 14, 1893, at the Smithsonian Institution with a light Robinson anemometer

(paper cups) registering every revolution,
Abscisse = Time.

Ordinates = Wind velocities in miles per hour.

PLATE IIt

'

jzhio" PM u™ iz” 13” 14” 15” 16™ 17™ 18” 19” 20"
Wind velocities recorded February 4, 1893, at the Smithsonian Institution with a light Robinson anemometer
(paper cups) registering every revolution.
Abscisse = Time.

Ordinates = Wind velocities in miles per hour.

PLATE Iv,

sree fea

WIND : NORTHWEST.

_|

7)
12"z0™ z1™ 2e™ 23™ ea™ 25™ 26” 27" 28™ 2s” 30”

Wind velocities recorded February 4, 1893, at the Smithsonian Institution with a light Robinson anemometer
(paper cups) registering every revolution.
Abscisse = Time.

Ordinates = Wind velocities in miles per hour.

PLATE V

| |

WIND. NORTHWEST

Wind velocities observed at Smithsonian Institution February 20, 1893, with a
Robinson anemometer (aluminum cups) registering every five revolutions.
Abscisse = Time,

Ordinates = Wind velocities in miles per hour.

H

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE
VOLUME 27. NUMBER 3

Part I. 1887 To 1896

BY

~ SAMUEL PIERPONT LANGLEY

EDITED BY CHARLES M. MANLY ah

Part IL. 1897 TO 1903

BY
CHARLES M. MAN Ng

Assistant in Charge of Experiments

5 (PUBLICATION 1948)

CITY OF WASHINGTON
PUBLISHED BY THE SMITHSONIAN INSTITUTION
1911

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

VOLUME 27. NUMBER 3

LANGLEY Memoir ON MECHANICAL FLIGHT

Part I. 1887 To 1896

BY

SAMUEL PIERPONT LANGLEY

EDITED BY CHARLES M. MANLY

Part II. 1897 To 1903

BY
CHARLES M. MANLY

Assistant in Charge of Experiments

A. ouan lasting
S 239267
MAY 20 1914

/
. ae
Office LipratL-

(PUBLICATION 1948)

CITY OF WASHINGTON
PUBLISHED BY THE SMITHSONIAN INSTITUTION
1911

Commission to whom this Memoir
has been referred:

Orro Hinearp Tirrman,
GEORGE OWEN Squier,
Apert Francis ZAHM.

The Lord Baltimore Press

BALTIMORE, MD., U. 8. A.

SS. 2a

ADVERTISEMENT

The present work, entitled ‘‘ Langley Memoir on Mechanical Flight,’’ as
planned by the late Secretary Samuel Pierpont Langley, follows his publications
on ‘‘ Experiments in Aerodynamics ’’ and ‘‘ The Internal Work of the Wind ”’
printed in 1891 and 1893, respectively, as parts of Volume 27 of the Smithsonian
Contributions to Knowledge.

This Memoir was in preparation at the time of Mr. Langley’s death in 1906,
and Part I, recording experiments from 1887 to 1896, was written by him. Part
II, on experiments from 1897 to 1903, has been written by Mr. Charles M. Manly,
who became Mr. Langley’s Chief Assistant in June, 1898. The sources of infor-
mation for this Part were the original carefully recorded accounts of the experi-
ments described,

It is expected later to publish a third part of the present memoir, to consist
largely of the extensive technical data of tests of the working of various types of
curved surfaces, propellers, and other apparatus.

It is of interest here to note that experiments with the Langley type of aero-
drome * did not actually cease in December, 1903, when he made his last trial
with the man-carrying machine, but as recently as August 6, 1907, a French
aviator made a flight of nearly 500 feet with an aerodrome of essentially the same
design. (See Appendix.)

In accordance with the established custom of referring to experts in the
subject treated, all manuscripts intended for publication in the Smithsonian
Contributions to Knowledge, this work was examined and recommended by a
Commission consisting of Mr. O. H. Tittman, Superintendent of the United
States Coast and Geodetic Survey, who witnessed some of the field trials, George
O. Squier, Ph. D. (Johns Hopkins), Major, Signal Corps, U. S. Army, and Albert
Francis Zahm, Ph. D., of Washington City.

Cartes D. Watcort,
Secretary of the Smithsonian Institution.

1The name “aerodrome” was given by Secretary Langley to the flying machine in 1893, from
depodpouéw (to traverse the air) and depodpéyoc air runner.—Internal Work of the Wind, p. 5.

are

PREFACE

The present volume on Mechanical Flight consists, as the title-page indi-
cates, of two parts. The first, dealing with the long and notable series of early
experiments with small models, was written almost entirely by Secretary Lang-
ley with the assistance of Mr. E. C. Huffaker and Mr. G. L. Fowler in 1897. Such
chapters as were not complete have been finished by the writer and are easily
noted as they are written in the third person. It has been subjected only to such
revision as it would have received had Mr. Langley lived to supervise this pub-
lication, and has therefore the highest value as an historical record. The com-
position of the second part, dealing with the later experiments with the original
and also new models and the construction of the larger aerodrome, has neces-
sarily devolved upon me. This is in entire accordance with the plan formed by
Mr. Langley when I began to work with him in 1898, but it is to me a matter of
sincere regret that the manuscript in its final form has not had the advantage of
his criticism and suggestions. If the reader should feel that any of the descrip-
tions or statements in this part of the volume leave something to be desired in
fullness of detail, it is hoped that some allowance may be made for the fact that
it has been written in the scanty and scattered moments that could be snatched
from work in other lines which made heavy demands upon the writer’s time and
strength. It is believed, however, that sufficient data are given to enable any
competent engineer to understand thoroughly even the most complicated phases
of the work.

Persons who care only for the accomplished fact may be inclined to under-
rate the interest and value of this record. But even they may be reminded that
but for such patient and unremitting devotion as is here enregistered, the now
accomplished fact of mechanical flight would still remain the wild unrealized
dream which it was for so many centuries.

To such men as Mr. Langley an unsuccessful experiment is not a failure but
a means of instruction, a necessary and often an invaluable stepping-stone to the
desired end. The trials of the large aerodrome in the autumn of 1903, to which
the curiosity of the public and the sensationalism of the newspapers gave a char-
acter of finality never desired by Mr. Langley, were to him merely members of
a long series of experiments, as much so as any trial of one of the small aero-
dromes or even of one of the earliest rubber-driven models. Had his health and
strength been spared, he would have gone on with his experiments undiscouraged
by these accidents in launching and undeterred by criticism and misunder-

standing.

VI ’ PREFACE

Moreover, it is to be borne in mind that Mr. Langley’s contribution to the
solution of the problem is not to be measured solely by what he himself accom-
plished, important as that is. He began his investigations at a time when not
only the general public but even the most progressive men of science thought of
mechanical flight only as a subject for ridicule, and both by his epoch-making
investigations in aerodynamics and by his own devotion to the subject of flight
itself he helped to transform into a field of scientific inquiry what had before
been almost entirely in the possession of visionaries.

The original plans for this publication provided for a third part covering
the experimental data obtained in tests of curved surfaces and propellers. Ow-
ing to the pressure of other matters on the writer, the preparation of this third
part is not yet complete and is reserved for later publication.

Crarues M. Manuy.
New York City.

CHAPTER
Lp
15

Ill.

\WAle

VEE

VIII.

IX.

II.
IIL.

CONTENTS

PART |

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History of construction of frame and engines of aerodromes...........-....-..++05:
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BSS Gea aera ee acs ar Me Sich c, su fohesaae sauces aeoyests Weaya or epalcyecere Tene ersten rsetats
History of construction of sustaining and guiding surfaces of aerodromes 4, 5, and 6.
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History of launching apparatus and field trials of aerodromes 4, 5, and 6...........-
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Description of the launching apparatus of aerodromes Nos. 5 and 6..............---+
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Condensed record of flights of aerodromes Nos. 5 and 6, from June 7 to August 3,
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123
128
133

135
135
137
139
140
140
141
142
143
144
145
146
147
148
149

vu CONTENTS

PART II—Continued

CHAPTER PAGE
IV. House-boat and launching apparatus...........-.. eee eee ee eee etter eet e eee Sevatsarerae 156

V. Construction of frame of large aerodrome...........-..---ee cece etree eee eens esees 164
TrAaNSVerse MIAME! <.cccvevaicfoe = cvelels ole selel ope iescieetel ots wl deleted) Levee) olats)aleketsiataieleyalolelalni=ialesiei 174

Propellers) vor er aucrs cise wickstesovonapetar este ofeVolepe hehehene ogeliarel (eve rinkekee=tnte aleketalel fot exe pated eels

PS ath TC) een E OD ee OOO soto Onno dob Conor oUdErt=dca5OUOg Abin conse LO 185

VI. Construction of supporting surfaces...... 2.2... -- eee eee eee ee ce ete e ee tec e ee tn ees 188
VII. Equilibrium and control. ..........00000+ ccc cee eee c ese ener ne nese ene ewecenencre 207
VIII. The experimental engine...........2.25- cece eee eee cere e eter cnnncens 218
IX. The quarter-size model aerodrome.........---..2+-- ss eeee reece eet eset eet teens 226

X. Construction and tests of the large engine....-...-...- see eee eee et eee teen renee eee 234

XI. Shop tests of the aerodrome........-2.-- 1-1 ee eee nee ee eet tet e nee tees esees 251
MT. Wield! trials: tin 190 8%... «ocx cccieveseveberelovesetotete obotele ene epere fel eievetebe eeVokel= tele \-latntndasaele lola letedalnialetieintate 255
Statement made by Mr. Manly to associated press .....----++++-ee-eeeeeeeeeeees 266

Report of War Department, January, 1904 .......-..---2- sees eee ee eect eee sees 276

Langley aerodrome, Official Report of Board of Ordnance, October, 1904........... 278

Statement ‘to. the! Pressivec- «sme vie cers ce craletoleinre ctels ote tinue (nYasie io Cayale) =| afe fale tetahetny latetetalatarere 280

Present) status Of the worker cereal ote eile ake etcteiele eiete teltelotele re tet a oke tote T= =Foteele acim eebae ic Rats ieas 281

Blériot Machine of 1907 on Langley type ...........------ eee e eee eee eeee Sitimaheta oie 283

Appendix. Study of American Buzzard and “John Crow Da icleyere ne teas oe ee Be aisle eeiere 285
TNStructions! CO. ASSISUANUS eerie ereleseetetelets ete eietole cates lete = palcsle ele tetera tan teu ataxia arena 294

Datasheets satis a\ cvctecsraere caceteerarl teed etre etcetera otal ae ee cee ta eae stellate Ye tele oe te 297

End exrrertacicteceit: ee ee ee ERAT OR TAD UT CIDA OM OCCUR KC SOMOS OaA GO OS A aenoneconens 309

LIST OF PLATES

PLATE PAGE
1. Rubber-motor model aerodromes Nos. 11, 13, 14, 15, 26, 30, 31...................-.....-. 16
PRET DEL UOLOLe MOU. AeTOUTOMES) INOSie du, LS od csc ecslatorepeeteretene¥ere cutenae ieyeteiedetalerei sieve stots) s)els 16
oe Rubber-motor model aerodromes NOs: 15) 24. ci cies wale mv nieieiel vices elercivie/elcucinicinlcwwfale lb vie = of 16
Ae HELM OLOLEMOC Sl ACLOUTOMOe NOs 12 Olstelareletaie cle le) efticliclerehel oleic) kelitieie aie ele slat onc ei efeieraleitelaictscielele 16
Pee Lu beL-pullmmOCels ACT OCLOME aiytaretsre acta ol chats alle lsymtcpelele/elehanohaciielotepshelatelalerohei at -calalehet etal shea sie)! xtelia)/= 24
LUD DEL-DUllemOG Ol ACLOOTOMNIG sc.) ciacs.crncyele afereio/auctoleleiot=afer eoheiatalstebelol olatche late ieletarefete t= etatanaa/e) elalenol 24
TEER DNEL-DUll MOTE TACKOOLOMIC sa) cies se ait. = viele intele cierelotclelele clerolefolninteralie’e sfelaleleYele|orelol>|-j<iareieneiel 24
SLU VeL-PUllsmOdel ACLOALOME s.r. wien oie ew nie, oiciei viele) ebeyaelelalo/a ele alae! sha) oialaisjeieiol« (oe \eleieiaiarela\ 24
9. Rubber-pull model aerodrome. ...... 22.2... ee ee cee cee eee ete tees ewer ereene 24
10. Steel frames of aerodromes Nos. 0, 1, 2, 3, 1891 and 1892............................ 33
11. Steel frames of aerodromes Nos. 4, 5, 6, 1893, 1895, and 1896......................... 53
12. Burners, acolipiles, amd separators... .. 2... cece cece eee ce ee tee ence renee sent eeseees 56
PPE OME SEOLACLOULOULOS sisteter aisles icleyerstere sister elie cle alelorals cuelofe cleke] elo) tie'e) sieiensiletetploysicts m= "oun laipraliofelelelaie 56
14. Aerodrome No. 5, December 3, 1895. Plan view. Rudder removed..........-...------ 78
15s Aerodrome: No. 5, December’ 3; 1895. Side View <2 2s .-.0..6 260 es 5s cee nels eras asec 78
16. Early types of wings and systems of guying.........-...e eee eee rete eee reece enc eeces 81
17. Aerodrome No. 5. Plan of wings and system of guying...............--+-++s+-++-ees 89
18. House-boat with overhead launching apparatus, 1896 ................seeeceeeer ee eeees 106
19. Paths of aerodrome flights, May 6 and November 28, 1896, near Quantico, Va., on the
POCO MAGEE U VC recreipetnieteteteni ciccehsvirr cs fev arel cas iovef eireter i ayiel a/aie\cNaloueteketeVelsteonabeteisleta¥e) eratatetaselelenelae 108
20. Instantaneous photograph of the aerodrome at the moment after launching in its flight
at Quantico on the Potomac River, May 6, 1896. Enlarged ten TIM GS ore ators wicks 108
21. Instantaneous photograph of the aerodrome at a distance in the air during its flight at
Quantico on the Potomac River, May 6, 1896. Enlarged ten TINCT contac tele rtae oins 108
22. Instantaneous photograph of the aerodrome at a distance in the air during its flight at
Quantico on the Potomac River, May 6, 1896. Enlarged ten times........-...----- 108
8. Overhead launching apparatus... ... 66.5. cee eee eee ee mee eme ee ee ssc ees se eecee 108
94. Overhead launching apparatus. ... 0... cc eee cee ee eee eee etre rnc er teres cerics 108
25. Side view of steel frame of aerodrome No. 5 suspended from launching-car, October 24,
BAO ep a I oe enon ed um renee cs set aaheiavel onevel opel oi sialerste] exetal sveqotelniehstansyeruntensie ol saverate 112
26A. Dimensioned drawing of boiler coils, burners, pump, needle valve, and thrust bearing... 116
°6B. Dimensioned drawing of engine No. 5.........--0- sees e see e ret t ete t ere t etc csees 116
27A. Side and end elevations of aerodrome No. 5, May 11, 1896......------+++++-es+eeee reese 116
27B. Aerodrome No. 5. Plan view. October 24, 1896 .......--.eeeeeees eter tree eee e tet eees 116
28. Steel frame of aerodrome No. 6 on launching Car .....---se see se reeset etre sees esses 120
299A. Plan view of aerodrome No. 6. October 23, 1896 .......----seeee erste rere este te eee 122
29B. Side elevation of aerodrome No. 6. October 23, 1596 ......---s reese settee eter steers 122
30. Plan view of steel frames and power plants of aerodromes Nos. 5 EW Ine ge eo ud.o BAGODKe 122
Tie atal ls OfPACLOGLOMEYNO Mon caw seis sree <leres ee wlele © infers slol=)-1= /=1 ore 108 Ime irises emesis 122 |
32. Drawings of proposed man-carrying aerodrome, NRO Sheets te chencre rede srat Neretakeole mere getetterete interes 130 |
33. Path of flight of aerodrome No. 6, June 7, TRCN Pen oS ho DnO ORS OO GU DD COnSOOH Ofac tO chbO Or 136 i
34. Paths of flight of aerodrome No. 6, June 13 and OP nItem pe prp Gouna cooC oe ubool OC onDr 140
Bre GrOdrOmen NON 5 One lAUNChINS Way Sia. crri-- o1-)-telm elon ieleinial-in1njn ein rele Seles ores i=iciniclcleha cia 142 |
36. Paths of flights of aerodrome No. 5, July 29, 1899 ...-.---+++sseerrr rere ester testes 148 f
37. Experiméntal forms of superposed surfaces, 1898, 1899. (See also plates 64 and 65.).... 153
38. Houseboat and launching apparatus, 1899.........---+--sess retest 156 \
89. Method of attaching guy-wires to guy-posts to relieve torsional strain........--+----.++-- 158 |
40. General plan and details of launching-car......------++-+ecrert retest tet 160 |
a peueNerouromeront lalnchine-Caneg 3.i1se 5 aloe et sieiere elera nielim lon ce = poles i es Gs 160 |
42. Details of clutch-post for launching-car......---+--++s-serr ett ee 160 .
43. Front end of track just preparatory to launching ACTOGTOME ...-.--e seer eerste 160
Mileereeistance;oG wites at elven) VElOCILICS) <0.) este moment? See oe a 166
AG. Frame of aerodrome A, January 31, 1900....--.+++sesserrecnrrsenscns etme e ees i
46. Brame of aerodrome A, January 31, 1900. ...-+.+.seceerecrrrererecersecrssscus estes” a
47. Frame of aerodrome A, February 1, 1900....+---+++- DoH Ucn Cade mddODUpUGUDOTIOU CT OOUDL ee '
48, Frame of aerodrome A, February 1, 1900....-+ssseeceeccessrsserssecsrercrsssere ess se® |

x LIST OF PLATES

PLATE PAGE
49: (Guy-wire system, July LOS 1902 role cole sielei~(eielaloleiale eLavarahspavere’ a/a,sia/=:siese. terete ler eeetete See 170
50. Guy-wire system, July 10, 1902... 0... 6. oie ccc ie eee ieee nen nr nnn w enn amereruescesss 170)
51. (Guy-wire system; July 05902 neers acre ele petedee ete ater ol ole pled elie stetielie dete V-nt= tata abated olin atale eee 170
52. Scale drawing of aerodrome A. End elevation ..............ee cece eee e ene e ee neceenne 170
58. Scale drawing of aerodrome A. Side elevation ............00esee eee eee e weet eneee ‘ 170
b4.. ‘Scale drawing ofvacrodrome; As (Tam a. ereter-ietencrcretarslereraleereke = brane se teed oh ated alates nen eet 170
55. Frame fittings and guy-wire attachments, etc...........2..-2 2 ese eee ete ee enter ne eeee 174
56. Frame fittings and guy-wire attachments, etc...........------- 2 eee eee eee eee tenes 174
57. Frame fittings and guy-wire attachments, etc............------ 2-22 eee eee sete e teen eens 174
58. Bed! plate’ fears: ete cc onc 5 soo cere, owe svasste a cleo sein eave ialatointelote) x ola laietelolel= wich ia alatial ers tabaietslalloter 176
59) Wine clamps cco 22lc ac crerejoe oes eseseters ete creh cle oho etaialstaNatove lave «lintels iol lel-tinteX= (et ai atta et aia otatats Steainran 183
60: Hoistine aerodrome. to Vaumchiine-trache spec arches teeta) eis letn ie otal ctal= efole clara etalon = iatet- al tial atatsi dn ietalaln 184
61. Aerodrome on launching-car; front wings in place, guy-wires adjusted.................. 184
62.: Details. of ‘sury-DOsts < 55 oo .'e Ae srerelsinl ere weeiate tevate fe oe els Cab Deke penal atal= hes elin allo lee elit othe atehsTeatelio iste 184
63: Guy-post and) pin: On Jaumehin e-came ie esc ieiectstore we reteie ic lele eete eel otatet ats pedaliete oh elo) shelton tale = Tat etal s Isiel ate 184
64. Experimental type of superposed wings, March 2, 1899................2..-eee- essences 192
65. Experimental type of superposed wings, March 2; 18990 <7. c2 2. cose oe we oe eine einiwienin= 192
662 “Detailsvof ribsand fittings Tor qyime seers cc cknedelcoeceteielseee erate Sap A slateye SuetenLetMefel otetetetohniate 200
6%: Cross-section: ‘Of VIDS r.6 7 sects etme ote ee ncre elie he foie epee area Crete RN ey steve roca ate re Bese eet toe ose eee 201
68) ‘Automatic: equillibritim de viceseye cere ctey el ircretetie to tena tact eaettet ele o etctes ele tee ela al adele ts elie aeto i 212
69, ‘Mechanism ‘Of: Controls icc crercetescterc cre nisrelatetal ores wis hein het reheat ects lleieyeyette ie wreiele aie et oe skola 212
70. Plan view of quarter-size model aerodrome, June 1, 1900..................-.-.-2---0- 232
Td. Plan view of quarter-sizesmodel aerodrome. seeeisiies ile ere eleiacielos siete alee eit eee 232
72. End, side, and three-quarter elevations of quarter-size model aerodrome...............-- 232
i3;. Lawnehinge-car swith) floats cert crm: stele raterus eta loheiolelarn ie atelet skate lo chaleleta ate Rets te intel eta DO REAa SOS 232
W45 Launchine-car with) floats ose ceca ate te coatovars roots toeicle atctoteteteke eiotete ie erate ats ate fntefaliay.elapiatels ani tatatetals 232
75. Quarter-size model aerodrome equipped with superposed surfaces, June 11, 1901. Side
VIEWS ieye Sic, crevafars toc aceleie ta eteyosclets els, oworetadahsvepeds sieseiolasasei snaps iatele fol oietels tel ketakete) deter stehatsRetetete ts ietanaln 232

76. Quarter-size model aerodrome equipped with superposed surfaces, June 11, 1901. End
WL OWS <5 rains 0: ayege ava seseloveiaearer veers uarevowe, tebe’ cheteteneya araateu tats (auahat cles aie) ale pevshereharote tenements Reteles ketenes 232
77. Cylinders of engine of quarter-size model aerodrome ..............-22-eeeeceeeeceeees 233
78. Engine of aerodrome A. Section through cylinder and drum...................+++-0+: 236
79. Engine of aerodrome A. Hind’ elevation, port Side -oc o occ cie ene ine e ne pe ole w nelle = in reisl! 236
805 sHngine/of acrodromerAy Voy) ple crereysrestetoreuereyeecatete lave releie le) steele teno deta lotetets inlet sie tevehel =a etetetanelate 236
81. Engine of aerodrome A. Elevation starboard bed plate, sparking mechanism........... 236
82. Dynamometer tests’ of arse: emainet nae. c.crctcserere eein stereo oenerereveteltehoraioge eee tenstonente ler ieaerte 248
83: Dynamometer ‘tests of Yarzeensines. occa = sete cie ese le cleric ieee eee Hoes Sere 248
84. (Dynamometer, tests ‘of largeveneine’ 5...) csc ccc terrors ere selevereesiears siete ela aerate ve lelinl oisteretle 248
85. Location of house-boat in center of Potomac River, July 14, 1903....................--- 256
86. Quarter-size model aerodrome mounted on launching-car ................2ccc eee neeeees 260
87. Quarter-size model aerodrome in flight, August 8, 1903...... 2... 2.2 oc ele w weeees 260
88. Quarter-size model aerodrome in flight, August 8, 1903..............5....sseesscescees 260
89. Quarter-size model aerodrome in flight, August 8, 1903....................-sseseseuees 260
90. Quarter-size model aerodrome in flight, August 8, 1903......................+.....000: 260
91. Quarter-size model aerodrome in flight, August 8, 1908......................--..e5eees 260
92! (Quarter-size: model ‘aerodrome in) flight) -Ageuste ss) 0 Ooi ete tere aerate ie mie elie een rere rere 260
3. Quarter-size model aerodrome at end of flight, August 8, 1903...................-2+--2> 260
94: Hoistine wines of full-sizeraerodrome’ ia ccecrcrorets <tele ake aint enero terete tiene tet kel aatey eiee ree ee eae 263
9b) Plight of large aerodrome October 7s 1G 0 Serer sere (cteyete cect tere terete sete renee etait teeter 266
96: Plight ‘of largeaecrodromie; October’ 7.) 90S ete aecse anieteeeiiee acted re eate ra ieie tenet 266
97. Aerodrome being recovered Octoperiity M90 deter atte iereteere easier ee rte eee 270
98:.. Aerodrome in’ water: (October 7; 1903 2.2. 5 2:. ecicsteis ois aes Spree atv ate tes ete reneiel <ieinfetovaicketsren eyes 270
99° ‘Aerodrome: in water: October’ 75/1903 occ iec carers ota ote le alo or acieiatn re eb ieeeeneseal fhe statist aie tetees 270
100. Aerodrome in’ water, “October 75 W903 % 2) <ccreiciwietelete ct tere rei oialereists sivioke neva) blake ee ater eae ieee 270

101. Attempted launching of aerodrome, December 8, 1903.....-...... ccc eeeceecececnceances 274

REFERENCES

Aerodynamics. See Langley, S. P. Experiments in Aerodynamics.

L’Aéronaute. See Pénaud, A.

Aeronautical Society. See Harting, P.

Aéroplane automoteur. See Pénaud, A.

Balancing of Engines, Steam, Gas, and Petrol. See Sharp, A.

Century Magazine. See Maxim, H. 8.

Comptes Rendus, of the Sessions of the Academy of Sciences. See Langley, S. P. Description du vol
méchanique.

Encyclopedia Britannica. See Flight and Flying Machines.

Experiments in Aerodynamics. See Langley, S. P.

Flight and Flying Machines. Encyclopedia Britannica, Sth ed., Vol. 9, 1879, Edinburgh, pp. 308-322,
figs. 1-45.

Harting, P. Observations of the relative size of the wings and the weight of the pectoral muscles in
the vertebrated flying animals. Annual Report of the Aeronautical Society of Great Britain,
No. 5, 1870, Greenwich, pp. 66-77.

Il nuovo aeroplano Blériot, Bollettino della Societa Aeronautica Italiana, Anno IV, N. 8, Agosto 1907,
Roma, pp. 279-282, figs. 4.

Langley, Bollettino della Societa Aeronautica Italiana, Anno II, Num. 11-12, Nov.-Dic. 1905, Roma, pp.
187-188, figs. 10.

Langley, S. P. Description du vol méchanique. Comptes Rendus de l’Académie des Sciences, T. 122,
Mai 26, 1896, Paris, pp. 1177-1178.

Langley, S. P. Experiments in Aerodynamics. Smithsonian Contributions to Knowledge, Vol. 27,
1891, Washington, D. C., pp. 115, pl. 10.

Langley, S. P. Le travail intérieur du vent. Revue de Il’Aéronautique, 6e année, 3e livraison, 1893,
Paris, pp. 37-68.

Langley, S. P. The Flying Machine. McClures Magazine, Vol. 9, No. 2, June, 1897, N. Y., pp. 647-660.

Langley, S. P. The Internal Work of the Wind. Smithsonian Contributions to Knowledge, Vol. 27,
1893, Washington, D. C., pp. 23, pl. 6.

McClure’s Magazine. See Langley, S. P. The Flying Machine.

Maxim, H.S. Aerial navigation. The power required. Century Magazine, Vol. 42, No. 6, Oct., 1891,
N. Y., pp. 829-836, figs. 1-6.

Pénaud, A. Aeroplane automoteur. L’Aéronaute, 5e année, No. 1, Jan., 1872, Paris, pp. 2-9, figs. 1-4.

Revue de l’Aéronautique. See Langley, S. P. Le travail intérieur du vent.

Sharp, A. Balancing of Engines, Steam, Gas, and Petrol. New York, Longmans, Green & Co., 1907.

Wellner, Georg. Versuche ueber den Luftwiderstand gewélbter Flichen im Winde und auf Wisen-
bahnen. Zeitschrift fiir Luftschiffahrt, Bd. 12, Beilage, 1893, Berlin, pp. 1-48.

Zeitschrift fiir Luftschiffahrt. See Wellner, Georg.

4)

LANGLEY MEMOIR ON MECHANICAL FLIGHT
PART JL 31887) TOP1 S96

BY 7S. .Ps GANGEEY

Epitep sy CHARLES M. MANLY

CHAPTER I
INTRODUCTORY

T’ announced in 1891,’ as the result of experiments carried on by me
through previous years, that it was possible to construct machines which would
give such a velocity to inclined surfaces that bodies indefinitely heavier than
the air could be sustained upon it, and moved through it with great velocity.
In particular, it was stated that a plane surface in the form of a parallelogram
of 76.2 em.x12.2 em. (304.8 inches), weighing 500 grammes (1.1 lbs.), could
be driven through the air with a velocity of 20 metres (65.6 feet) per second
in absolutely horizontal flight, with an expenditure of 1/200 horse-power, or, in
other terms, that 1 horse-power would propel and sustain in horizontal flight,
at such a velocity (that is, about 40 miles an hour), a little over 200 pounds
weight of such surface, where the specific gravity of the plane was a matter of
secondary importance, the support being derived from the elasticity and imer-
tia of the air upon which the body is made to run rapidly.

It was further specifically remarked that it was not asserted that planes of
any kind were the best forms to be used in mechanical flight, nor was it asserted,
without restrictions, that mechanical flight was absolutely possible, since this
depended upon our ability to get horizontal flight during transport, and to leave
the earth and to return to it in safety. Our ability actually to do this, it was
added, would result from the practice of some unexplored art or science which
might be termed Aerodromics, but on which I was not then prepared to enter.

T had at that time, however, made certain preliminary experiments with
flying models, which have been continued up to the present year,’ and at the
same time IT have continued experiments distinct from these, with the small
whirling-table established at Washington. The results obtained from the latter

99

being supplemental to those published in ‘‘ Experiments in Aerodynamics,’ and

1“ ®Hxperiments in Aerodynamics,” Smithsonian Contributions to Knowledge, Vol. 27, 1891.
?This chapter was written almost entirely by Mr. Langley in 1897.
51897.

2 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

being more or less imperfect, were at first intended not for publication, but for
my own information on matters where even an incomplete knowledge was better
than the absence of any.

It is to be remembered that the mechanical difficulties of artificial flight
have been so great that, so far as is known, never at any time in the history
of the world previous to my experiment of May, 1896, had any such mechanism,
however actuated, sustained itself in the air for more than a few seconds—
never, for instance, a single half-minute—and those models which had sustained
themselves for these few seconds, had been in almost every case actuated by
rubber springs, and had been of such a size that they should hardly be described
as more than toys. This refers to actual flights im free air, unguided by any
track or arm, for, since the most economical flight must always be a horizontal
one ina straight line,** the fact that a machine has lifted itself while pressed up-

rard against an overhead track which compels the aerodrome to move horizon-
tally and at the proper angle for equilibrium, is no proof at all of real ‘‘ flight.’’

I desire to ask the reader’s consideration of the fact that even ten years
ago, the whole subject of mechanical flight was so far from having attracted
the general attention of physicists or engineers, that it was generally considered
to be a field fitted rather for the pursuits of the charlatan than for those of the man
of science. Consequently, he who was bold enough to enter it, found almost none
of those experimental data which are ready to hand in every recognized and
reputable field of scientific labor. Let me reiterate the statement, which even
now seems strange, that such disrepute attached so lately to the attempt to
make a ‘‘ flying-machine,”’ that hardly any scientific men of position had made
even preliminary investigations, and that almost every experiment to be made
was made for the first time. To cover so vast a field as that which aerodromics
is now seen to open, no lifetime would have sufficed. The preliminary experi-
ments on the primary question of equilibrium and the intimately associated
problems of the resistance of the sustaining surfaces, the power of the engines,
the method of their application, the framing of the hull structure which held
these, the construction of the propellers, the putting of the whole in initial
motion, were all to be made, and could not be conducted with the exactness which
would render them final models of accuracy.

I beg the reader, therefore, to recall as he reads, that everything here has
been done with a view to putting a trial aerodrome successfully in flight within
a few years, and thus giving an early demonstration of the only kind which is
conclusive in the eyes of the scientific man, as well as of the general public—a
demonstration that mechanical flight is possible—by actually flying.

All that has been done, has been with an eye principally to this immediate

°° In this statement, of course, no account is taken of the “‘ internal work of the wind.”
“Ten years prior to 1897.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 3

result, and all the experiments given in this book are to be considered only as
approximations to exact truth. All were made with a view, not to some remote
future, but to an arrival within the compass of a few years at some result in
actual flight that could not be gainsaid or mistaken.

Although many experimenters have addressed themselves to the problem
within the last few years—and these have included men of education and skill
—the general failure to arrive at any actual flight has seemed to throw a doubt
over the conclusions which I had announced as theoretically possible.

When, therefore, I was able to state that on May 6, 1896, such a degree of
suecess had been attained that an aerodrome, built chiefly of steel, and driven
by a steam engine, had indeed flown for over half a mile—that this machine had
alighted with safety, and had performed a second flight on the same day, it was
felt that an advance had been made, so great as to constitute the long desired
experimental demonstration of the possibility of mechanical flight. These results
were communicated to the French Academy in the note given below.’

Independently of the preliminary experiments in aerodynamics already pub-
lished, I had been engaged for seven years in the development of flying models.
Although the work was discouraging and often resulted im failure,-success was
finally reached under the conditions just referred to, which obviously admitted
of its being reached again, and on a larger scale, if desired.

>Communication to the French Academy. Extract from the Comptes Rendus of the Sessions of

the Academy of Sciences, Vol. 122, Session of May 26, 1896.
(Translation. )
A Description of Mechanical Flight. By S. P. Langley.

In a communication which I addressed to the Academy in July, 1891, I remarked that the results
of experimental investigation had shown the possibility of constructing machines which could give
such a horizontal velocity to bodies resembling in shape inclined planes, and more than a thousand
times heavier than air, that these could be sustained on this element.

While I have elsewhere remarked that surfaces other than planes might give better results,
and that absolutely horizontal flight, which is so desirable in theory, is hardly realizable in
practice, so far as I know there has never been constructed, up to the present time, any heavy
aerodrome, or so-called flying-machine, which can keep itself freely in the air by its own force more
than a few seconds, the difficulties encountered in absolutely free flight being, for many reasons, im-
measurably greater than those experienced when the flight is controlled by the body’s pressing
upward against a horizontal track, or whirling-arm. No one is unaware that many experimenters
have been engaged in trying to execute free mechanical flight, and although the demonstration
which I furnished in 1891 [“ Experiments in Aerodynamics,” 1891] of its theoretical possibility with
means then at our disposition, seemed conclusive, so long a time has elapsed without practical results,
that it might be doubted whether these theoretical conditions are to be realized. I have thought it
well, then, to occupy myself with the construction of an aerodrome with which I might put my
previous conclusions to the test of experiment.

The Academy will, perhaps, find it interesting to read the narrative given here by an eye-witness,
who is well known to it. I am led to present it not only by the request with which he honors me,
but by the apprehension that my administrative duties may put a stop to these researches, so that
it seems to me advisable to announce the degree in which I have already succeeded, although this
success be not as complete as I should like to make it.

The experiments took place on a bay of the Potomac River, some distance below Washington.
The aerodrome was built chiefly of steel, though lighter material entered into the construction, so
that its density as a whole was a little below unity. No gas whatever entered into the construction of
the machine, and the absolute weight, independent of fuel and water, was about 11 kilos (24 pounds).
The width of the supporting surfaces was about 4 metres (13 feet), and the power was furnished by
an extremely light engine of approximately one horse-power. There was no one to direct it on
board, and the means for keeping it automatically in horizontal flight were not complete. It is

4 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

In view of the great importance of these experiments, as demonstrating
beyond question the practicability of the art of mechanical flight, and also in
view of the yet inchoate state of this art, I have thought it worth while to pub-
lish an account of them somewhat in detail, even though they involve an account
of failures; since it is from them, that those to whom it may fall to continue
such constructions, will learn what to avoid, as well as the raison d’etre of the
construction of the machines which have actually flown.

In an established art or science, this description of the essays and failures
which preceded full knowledge would have chiefly an historical terest. Here
almost nothing is yet established beyond the fact that mechanical flight has
actually been attained. The history of failure is in this case, then, if I do not
mistake, most necessary to an understanding of the road to future success, to
which it led, and this has been my motive in presenting what I have next to say
so largely in narrative form.

important to remark that the small dimensions of the machine did not allow it to include any
apparatus for condensing the steam, so that it could only carry water enough for a very brief
course—a drawback which would not be encountered in one of a larger construction.

It is also to be noted that the speed estimated by Mr. Bell was that obtained in a continuous
ascending flight, and much less than would have been attained in a horizontal course.

On Mechanical Flight. Letter of Mr. Alexander Graham Bell to Mr. Langley.
: Washington, May 6, 1896.

I am quite aware that you are not desirous of publication until you have attained more complete
suecess in obtaining horizontal flight under an automatic direction, but it seems that what I have
been privileged to see to-day marks such a great progress on everything ever before done in this way,
that the news of it should be made public, and I am happy to give my own testimony on the results
of two trials which I have witnessed to-day by your invitation, hoping that you will kindly consent
to making it known.

For the first trial, the apparatus, chiefly constructed of steel and driven by a steam engine,
was launched from a boat at a height of about 20 feet from the water. Under the impulse of its
engines alone, it advanced against the wind and while drifting little, and slowly ascending with a
remarkably uniform motion, it described curves of about 100 metres in diameter; till at a height
in the air which I estimate at about 25 metres (82 feet), the revolutions of the screws ceased for
want of steam, as I understood, and the apparatus descended gently and sank into the water, which
it reached in a minute and a half from the start. It was not damaged, and was immediately ready
for another flight.

In the second trial it repeated in nearly every respect the action of the first, and with an
identical result. It rose smoothly in great curves until it approached a prominent wooded promon-
tory, which it crossed at a height of 8 to 10 metres above the tops of the highest trees, upon the
exhaustion of the steam descending slowly into the bay, where it settled in a minute and thirty-one
seconds from the start. You have an instantaneous photograph of it, which I took just after the
launch. [See plates 20, 21, and 22 of present work.]

From the extent of the curves which it described, which I estimated with other persons, from
measurements which I took, and from the number of revolutions of the propellers, as recorded by
the automatie counter which I consulted, I estimate the absolute length of each course to be over
half an English mile, or, more exactly a little over 900 metres (2953 feet).

The duration of flight during the second trial was one minute and thirty-one seconds, and the
average velocity between twenty and twenty-five miles an hour, or, let us say 10 metres a second, ina
course which was constantly ascending. I was extremely impressed by the easy regular course of
each trial, and by the fact that the apparatus descended each time with such smoothness and
gentleness as to render any jar or danger out of the question.

It seemed to me that no one could have witnessed these experiments without being convinced
that the possibility of mechanical flight had been demonstrated.

CHAPTER II
PRELIMINARY

Part I of the present work is intended to include an account of the experi-
ments with actual flying models, made chiefly at or near Washington, from the
earliest with rubber motors up to the construction of the steam aerodromes that
performed the flights of May 6 and November 28, 1896.

An account of some observations conducted at Washington, with the whirl-
ing table, on the reaction of various surfaces upon the air, is relegated to a later
part.

The experiments with working models, which led to the successful flights,
were commenced in 1887, and it has seemed to me preferable to put them at first
in chronological order, and to present to the reader what may seem instructive
in their history, while not withholding from him the mistaken efforts which were
necessarily made before the better path was found. In this same connection,
I may say that I have no professional acquaintance with steam engineering, as
will, indeed, be apparent from the present record, but it may be observed that
none of the counsel which I obtained from those possessing more knowledge
was useful in meeting the special problems which presented themselves to me,
and which were solved, as far as they have been solved, by constant ‘‘ trial and
error.’’ :

I shall, then, as far as practicable, follow the order of dates in presenting
the work that has been done, but the reader will observe that after the prelimi-
nary investigations and since the close of 1893, at least four or five independent
investigations, attended with constant experiment and radically distinct kinds of
construction, have been going on simultaneously. We have, for instance, the
work in the shop, which is of two essentially different kinds: first, that on the
frames and engines, which finally led to the construction of an engine of un-
precedented lightness; second, the experimental construction of the supporting
and guiding surfaces, which has involved an entirely different set of considera-
tions, concerned with equilibrium and support in flight. These constructions,
however successful, are confined to the shop and are, as will be seen later, use-
less without a launching apparatus. The construction of a suitable launching
apparatus itself involved difficulties which took years to overcome. And, finally,
the whole had to be tested by actual flights in free air, which were conducted at
a place some 30 miles distant from the shop where the original construction

went on.

>) |

6 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

Simultaneously with these, original experiments with the whirling-table were
being conducted along lines of research, which though necessary have only been
indicated. We have, then, at least five subjects, so distinct that they can only
be properly treated separately, and accordingly they will be found in Chapters
VU, VI, LX and X, and in Part Third [in preparation].

It is inevitable that in so complex a study some repetition should present
itself, especially in the narrative form chosen as the best method of presenting
the subject to the reader. Each of these chapters, then, will contain its own
historical account of its own theme, so that each subject can be pursued continu-
ously in the order of its actual development, while, since they were all interde-
pendent and were actually going on simultaneously, the order of dates which is
followed in each chapter will be a simple and sufficient method of reference from
one to the other.

EXPERIMENTS WITH Smatui Mopexs

In order to understand how the need arises for such experiments in fixing
conditions which it might appear were already determined in the work ‘‘ Experi-
ments in Aerodynamics,’’? it is to be constantly borne in mind, as a considera-
tion of the first importance, that the latter experiments, being conducted with
the whirling-table, force the model to move in horizontal flight and at a constant
angle. Now these are ideal conditions, as they avoid such practical difficulties
as maintaining equilibrium and horizontality, and for this reason alone give
results more favorable than are to be expected in free flight.

> were obtained with

Besides this, the values given in ‘‘ Aerodynamics
rigid surfaces, and these surfaces themselves were small and therefore manage-
able, while larger surfaces, such as are used in actual flight, would need to be
stiffened by guys and like means, which offer resistance to the air and still
further reduce the results obtained. It is, therefore, fairly certain, that noth-
ing like the lift of 200 pounds to the horse-power for a rate of 40 miles an hour,’
obtained under these ideal conditions with the whirling-table, will be obtained
in actual flight, at least with plane wings.

The data in ‘‘ Aerodynamics ’’ were, then, insufficient to determine the con-
ditions of free flight, not alone because the apparatus compels the planes to move
in horizontal flight, but beeause other ideally perfect conditions are obtained by
surfaces rigidly attached to the whirling-table so as to present an angle to the
wind of advance which is invariable during the course of the experiment, whereas
the surfaces employed in actual flight may evidently change this angle and cause

It is desirable that the reader should be acquainted with the contents of this treatise, and of
another by me, entitled “ The Internal Work of the Wind,” both published by the Smithsonian Insti-
tution. A knowledge of these works is not absolutely necessary, but of advantage in connection with
what follows.

2“ Experiments in Aerodynamics,” p. 107.

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT . 7

the aerodrome to move upward or downward, and thus depart from horizontal
flight so widely as to bring prompt destruction.

To secure this balance, or equilibrium, we know in theory, that the center
of gravity must be brought nearly under the center of pressure, by which latter
expression we mean the resultant of all the forces which tend to sustain the
aerodrome; but this center of pressure, as may in fact be inferred from ‘‘ Aero-

” 3 varies with the inclination of the surface. It varies also with the

dynamics,
nature of the surface itself, and for one and the same surface is constantly
shifted unless the whole be rigidly held, as it is on the whirling-table, and as it
eannot be in free flight.

Here, then, are conditions of the utmost importance, our knowledge of which,
as derived from ordinary aerodynamic experiments, is almost nothing. A con-

sideration of this led me to remark in the conclusion of ‘* Aerodynamics ”’:

“‘T have not asserted, without qualification, that mechanical flight is prac-
tically possible, since this involves questions as to the method of constructing
the mechanism, of securing its safe ascent and descent, and also of securing the
indispensable condition for the economic use of the power I have shown to be
at our disposal—the condition, I mean, of our ability to guide it in the desired
horizontal direction during transport—questions which, in my opinion, are only
to be answered by further experiment and which belong to the inchoate art or
seience of aerodromics on which I do not enter.’’

It is this inchoate art of aerodromies which is begun in the following experiments
with actual flying machines.

_In all discussions of flight, especially of soaring flight, the first source to
which one naturally looks for information is birds. But here correct deductions
from even the most accurate of observations are very. difficult, because the
observation cannot include all of the conditions under which the bird is doing
its work. If we could but see the wind the problem would be greatly simplified,
but as the matter stands, it may be said that much less assistance has been de-
rived from studious observations on bird-flight than might have been anticipated,
perhaps because it has been found thus far impossible to reproduce in the fly-
ing machine or aerostatic model the shape and condition of wing with its flexible
and controllable connection with the body, and especially the instinctive control
of the wing to meet the requirements of flight that are varying from second to
second, and which no automatic adjustment can adequately meet.

At the time I commenced these experiments, almost the only flying-machine
which had really flown was a toy-like model, suggested by A. Pénaud, a young
Frenchman of singular mechanical genius, who contributed to the world many
most original and valuable papers on Aeronautics, which may be found in the
journal ‘‘ L’Aeronaute.’? His aeroplane is a toy in size, with a small propeller

*Chapter VIII.

8 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

whose blades are usually made of two feathers, or of stiff paper, and whose motive
power is a twisted strand of rubber. This power maintains it in the air for a
few seconds and with an ordinary capacity for flight of 50 feet or so, but it em-
bodies a device for automatically securing horizontal flight, which its inventor
was the first to enunciate.*

Although Pénaud recognized that, theoretically, two screws are necessary in
an aerial propeller, as the use of a single one tends to make the apparatus re-
volve on itself, he adopted the single serew on account of the greater simplicity
of construction that it permitted. One of these little machines is shown as No.
11, Plates 1 and 2.

AB is a stem about 2.5 mm. in diameter and 50 em. long. It is bent down at
each end, with an offset which supports the rubber and the shaft of the screw
to which it is hooked. The serew HH’ is 21 em. in diameter, and has two blades
made of stiff paper; two are preferable, among other reasons, because they can
be made so that the machine will lie flat when it strikes in its descent. About
the middle of AB there is a ‘‘ wing ’’ surface DC, 45 em. long and 11 em. broad,
the ends C and D being raised and a little curved. In front of the screw is the
horizontal rudder GK having a shape like that of the first surface, with its ends
also turned up, and inclined at a small negative angle with this wing surface.
Along its center is a small fin-like vertical rudder that steers the device later-
ally, like the rudder of a ship.

The approximately, but not exactly, horizontal rudder serves to hold the
device in horizontal flight, and its operation can best be understood from the
side elevation. Let CD be the wing plane set nearly in the line of the stem, which
stem it is desired to. maintain, in flying, at a small positive angle, a, with the
horizon, « being so chosen that the tendency upward given by it will just coun-
teract the action of gravity. The weight of the aeroplane, combined with the
resistance due to the reaction of the air caused by its advance would, under
these conditions, just keep it moving onward in a horizontal line, if there were
no disturbance of the conditions. There is, however, in the wing no power of
self-restoration to the horizontal if these conditions are disturbed. But such
a power resides in the rudder GK, which is not set parallel to the wing, but at
a negative angle (a') with it equal to the positive angle of the wing with the hori-
zon. It is obvious that, in horizontal flight, the rudder, being set at this angle,
presents its edge to the wind of advance and consequently offers a minimum
resistance as long as the flight is horizontal. If, however, for any reason the
head drops down, the rear edge of the rudder is raised, and it is at once subjected
to the action of the air upon its upper surface, which has a tendency to lower the
rear of the machine and to restore horizontality. Should the head rise, the lower

“His device for obtaining automatic equilibrium is found in connection with the description of
his “ Aeroplane Auto Moteur,” in “ L’Aeronaute” for January, 1872.

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 9

surface of the rudder is subjected to the impact of the air, the rear end is raised,
and horizontality again attained. In addition to this, Pénaud appears to have
contemplated giving the rudder-stem a certain elasticity, and in this shape it is
perhaps as effective a control as art could devise with such simple means.

Of the flight of his little machine, thus directed, Pénaud says:

‘* Tf the serew be turned on itself 240 times and the whole left free in a hori-
zontal position, it will first drop; then, upon attaining its speed, rise and perform
a regular flight at 7 or 8 feet from the ground for a distance of about 40 metres,
requiring about 11 seconds for its performance. Some have flown 60 metres and
have remained in the air 13 seconds.’ The rudder controls the inclination to
ascend or descend, causing oscillations in the flight. Finally the apparatus de-
scends gently in an oblique line, remaining itself horizontal.’’

The motive power is a twisted hank of fine rubber strips, which weighs 5
grammes out of a total of 16 grammes for the whole machine, whose center of
gravity should be in advance of the center of surface CD, as will be demonstrated
in another place. This device attracted little notice, and I was unfamiliar with
it when I began my own first constructions at Allegheny, in 1887.

My own earliest models employed a light wooden frame with two propellers,
which were each driven by a strand of twisted rubber." In later forms, the rub-
ber was enclosed and the end strains taken up by the thinnest tin-plate tubes,
or better still, paper tubes strengthened by shellae.

Little was known to me at that time as to the proper proportions between
wing surface, weight and power; and while I at first sought to infer the relation
between wing surface and weight from that of soaring birds, where it varies
from 4 to 1 sq. ft. of wing surface to the pound, yet the ratio was successively
increased in the earlier models, until it became 4 sq. ft. to 1 pound. It may be
well to add, however, that the still later experiments with the steam-driven
models, in which the supporting surface was approximately 2 sq. ft. to the
pound, proved that the lack of ability of these early rubber-driven models to
properly sustain themselves even with 4 sq. ft. of wing surface to the pound,
was largely due to the fact that the wings themselves had not been stiff enough
to prevent their being warped by the air pressure generated by their forward
motion.

During the years I presently describe, these tentative constructions were re-

*TI have never obtained so good a result as this with any rubber motor. S. P. Langley.

*One pound of twisted rubber appears, from my experiments, to be capable of momentarily
yielding nearly 600 foot-pounds of energy, but this effect is attained only by twisting it too far. It
will be safer to take at most 300 foot-pounds, and as the strain must be taken up by a tube or frame
weighing at least as much as the rubber, we have approximately 0.0091 as the horse-power for one
minute, or 0.091 horse-power for six seconds as the maximum effect, in continuous work, of a pound
of twisted rubber strands. The longitudinal pull of the rubber is much greater, but it is difficult to
employ it in this way for models, owing to the great relative weight of the tube or frame needed to
bear the bending strain. In either form, rubber is far more effective for the weight than any steel
spring (see later chapter on Available Motors).

10 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

newed at intervals without any satisfactory result, though it became clear from
repeated failures, that the motive power at command would not suffice, even for
a few seconds’ flight for models of sufficient size to enable a real study to be made
of the conditions necessary for successful flight.

In these earliest experiments everything had to be learned about the relative
position of the center of gravity, and what I have called the center of pressure.
In regard to the latter term, it might at first seem that since the upward pres-
sure of the air is treated as concentrated at one point of the supporting surface,
as the weight is at the center of gravity, this point should be always im the same
position for the same supporting surface. This relation, however, is never con-
stant. How paradoxical seems the statement that, if ab be such a supporting
surface in the form of a plane of uniform thickness and weight, suspended at ¢
(ac being somewhat greater than ch) and subjected to the pressure of a wind in
the direction of the arrow, the pressure on the lesser arm cb will overpower that

a Osis

oo

Fic. 1. Diagram of suspended plane showing position of C. P.

on the greater arm ac! We now know, however, that this must be so, and why,
but as it was not known to the writer till determined by experiments published
later in ‘¢ Experiments in Aerodynamics,’’ all this was worked out by trial in
the models.

It was also early seen that the surface of support could be advantageously
divided into two, with one behind the other, or one over the other, and this was
often, though not always, done in the models.

At the very beginning another difficulty was met which has proved a con-
stant and ever-increasing one with larger models—the difficulty of launching
them in the air. It is frequently proposed by those unfamiliar with this difficulty,
to launch the aerodrome by placing it upon a platform car or upon the deck of
a steamer, and running the ear or boat at an increasing speed until the aerodrome,
which is free to rise, is lifted by the wind of advance. But this is quite imprac-
ticable without means to prevent premature displacement, for the large surface
and slight weight renders any model of considerable size unmanageable in the
least wind, such as is always present in the open air. It is, therefore, necessary
in any launching apparatus that the aerodrome he held rigidly until the very mo-
ment of release, and that instant and simultaneous release from the apparatus

be made at all the sustaining points at the proper moment.

—
’

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 1

There is but a very partial analogy in this case to the launching of a ship,
b

which is held to her ways by her great weight. Here, the ‘‘ ship ’’ is liable to rise
from her ways or be turned over laterally at any instant, unless it is securely
fastened to them in a manner to prevent its rising, but not to prevent its
advancing.

The experiments with rubber-driven models commenced in April, 1887, at
the Allegheny Observatory, were continued at intervals (partly there, but chiefly
in Washington) for three or four years, during which time between thirty and
forty independent models were constructed, which were so greatly altered in the
course of experiment that more nearly one hundred models were in reality tried.
The result of all this extended labor was wholly inconclusive, but as subsequent
trials of other motors (such as compressed air, carbonic-acid gas, electric bat-
teries, and the like) proved futile, and (before the steam engine) only the rubber
gave results, however unsatisfactory, in actual flight, from which anything could
be learned, [I shall give some brief account of these experiments, which preceded
and proved the necessity of using the steam engine, or other like energetic motor,
even in experimental models.

An early attempt was made in April, 1887, with a model consisting of a frame
formed of two wooden pieces, each about 1 metre long and 4 centimetres wide,
made for lightness, of star-shaped section, braced with cross-pieces and carrying
two long strips of rubber, each about 1 mm. thick, 30 mm. wide, 2 metres long,
doubled, weighing 500 grammes. Hach of these strips could be wound to about
300 turns, one end being made fast to the front of the frame, the other to the shaft
of a four-bladed propeller 30 em. in diameter. The wings were made of lightest
pine frames, over which paper was stretched, and were double, one being super-
posed upon the other. Each was 15 em. wide, and 120 em. long. The distance
between them was 12 cm. and the total surface a little more than 3600 sq. em.
(4 square feet). In flying, the rubber was so twisted that the propellers were run
in opposite directions. The weight of the whole apparatus was not quite 1 kilo-
gramme, or about 1 pound to 2 feet of sustaining surface, which proved to be
entirely too great a weight for the power of support. When placed upon the
whirling-table, it showed a tendency to soar at a speed of about ten miles an
hour, but its own propellers were utterly insufficient to sustain it.

In this attempt, which was useful only in showing how much was to be learned
of practical conditions, the primary difficulty lay in making the model light
enough and sufficiently strong to support its power. This difficulty continued to
be fundamental through every later form; but besides this, the adjustment of the
center of gravity to the center of pressure of the wings, the disposition of the
wings themselves, the size of the propellers, the inclination and number of their
blades, and a great number of other details, presented themselves for examina-

12 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

tion. Even in the first model, the difficulty of launching the machine or giving it
the necessary preliminary impulse was disclosed—a difficulty which may perhaps
not appear serious to the reader, but which in fact required years of experiment
to remove.

By June, 1887 two other models, embodying various changes that had sug-
gested themselves, had been constructed. Each of these had a single propeller
(one an 18}-inch propeller with eight adjustable blades, the other a 24-inch pro-
peller with four adjustable blades) and was sustained by two pairs of curved
wings 4 feet 7 inches long. It is, however, unnecessary to dwell further on these
details, since these models also proved altogether too heavy in relation to their
power, and neither of them ever made an actual flight.

At this period my time became so fully occupied with the experiments in
aerodynamics (which are not here in question) that during the next two years
little additional was done in making direct investigations in flight.

In June, 1889, however, new rubber-driven models were made in which the
wooden frames were replaced by tubes of light metal, which, however, were still
too heavy, and these subsequently by tubes of paper covered with shellac, which
proved to be the lightest and best material in proportion to its strength that had
been found. The twisted rubber was carried within these tubes, which were made
just strong enough to withstand the end-strain it produced. The front end of
the rubber being made fast to an extremity of the tube, the other end was at-
tached directly to the shaft of the propeller, which in the early models was still
supplied with four blades.

A detailed description of one of these early models, No. 26, shown in Plates
1 and 4, follows:

In each of the two tubes of paper, stiffened with shellac, which form a part
of the framing, is mounted a hank of twisted rubber, which connects with a pro-
peller at the rear. There are two pairs of wings, superposed and inclined at
an angle, the one above, the other below the frame. A light stem connected
with the frame bears a triangular Pénaud tail and rudder.

eneth" of; model Scr cira screens SiGe cfotescaree areas eer teens 105 cm.
Spredd’ ‘of Wwinessseiiccte = aucie ones oteeve sisleiare Pe ayers aictetaia tans tenererene 83°
Width: of upper Win eset stacialaisic: o eveccain-a «rere wee cle ee menere ieee 1a
Width ‘of lower WINES) oiciak succierstete sete aluiarelajais she clnieletensverstovere 19S
Diameterof propellers. 2 ie cee oe ec ee eteete A
Area Of MPDeEL, WINES 2-015, csertaasoictes slacva alate eieis teteone ee eae 1134 sq. em.
Area OL lower WANES’ ci r.os aoe 2/4 «tere tao scre erage tate ies ee ene: 1548 “
Area, OF tall sis cise dierecsisys.ite iss ste eiais.oles oe slot cele eokb ieee 1440 0%
Weightiof win ese... cic ie.cicc ciecotie airiemiced ureelereeetetatey tetera ate 51 grammes
Weileht of: Calls ca rstciecavs taSerre setae toleeottis inte tate oretote seater ereiakev oversi= to
Welghtiofframe:. <tc)... srs eet eee tenn en IIe reIerS Oona
Welght ‘of wheelsis i). chica cis cc-crse clam «a oisvelalapeinral cataiatoletavePene 20 *
Weight of rubber, (209) poundl)'sc2< =r. ctevteiste tes tele ere elaine 40 “
"Total, wel gities x..cie fe cca tcteratevarstteiehosesecekoreimae NepereNeteene ere Seer Tbe S

No: ‘of ‘turns ofsrub bers scctec eae - etestae a7 eins cin tee aie 100

Time of running downs oo... 6 .ci «ce reins eles ee leeisioicleroiwis wien 8 seconds

Horse-power from preceding data. ............s.escesecees 0.001 HP

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 13

The aerodromes made at this time were too heavy, as well as too large, to
be easily launched by hand, and it was not until 1891 that the first one was con
structed light enough to actually fly. This first flight was obtained from the
north window of the dome of the Allegheny Observatory, on March 28, 1891, and
imperfect as it was, served to show that the proper balancing of the aerodrome
which would bring the center of gravity under the center of pressure, so as to
give a horizontal flight, had yet to be obtained.

From this time on until 1893, experiments continued to be made with rub-
ber-driven models, of which, as has been stated, nearly 40 were constructed,
some with two propellers, some with one; some with one propeller in front and
one behind; some with plane, some with curved, wings; some with single, some
with superposed, wings; some with two pairs of wings, one preceding and one
following ; some with the Pénaud tail; and some with other forms. A few of these
early forms are indicated on the accompanying Plates 1 to 4, but it does not
seem necessary to go into the details of their construction.

No. 11 with which an early flight was made, closely resembles the Pénaud
model.

No. 13 has two propellers, one in front and one behind, with a single wing.

No. 14 has two propellers, nearly side by side, but one slightly in advance,
with a single wing and a flat horizontal tail.

No. 15 has one leading propeller and two broad wings, placed one behind
the other.

No. 30 has the propeller shafts at an angle, and one pair of wings.

No. 31 has the propeller shafts at an angle, and two pairs of wings super-
posed.

The wings in general were flat, but in some cases curved. The rubber was
usually wound to about 100 turns, and trouble continually arose from its ‘ kink-
ing ”’ and unequal unwinding, which often caused most erratic flights.

It is sufficient to say of these that, rude as they were, much was learned from
them about the condition of the machines in free air, which could never be learned
from the whirling-table or other constrained flight.

The advantages and also the dangers of curved wings as compared with
plane ones, were shown, and the general disposition which would secure an even
balance, was ascertained; but all this was done with extreme difficulty, since
the brief flights were full of anomalies, arising from the imperfect conditions of
observation. For instance, the motor power was apparently exhausted more
rapidly when the propellers were allowed to turn with the model at rest, than
when it was in motion, though in theory, in the latter case more power would
seem to be expended and a greater speed of revolution obtained in a given time.
The longest flights obtainable did not exceed 6 or 8 seconds in time, nor 80 to 100
feet in distance, and were not only so brief, but, owing to the spasmodic action
of the rubber and other causes, so irregular, that it was extremely difficult to
obtain even the imperfect results which were actually deduced from them.

14 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

ABBREVIATIONS AND SYMBOLS H/MPLOYED

The following rules and symbols were adopted for determining the relative
position of points on the aerodrome, some of them during 1891, and some of
them sinee. All are given here for convenience of reference, though their chief
application is to the larger steam aerodromes described later. Those which im-
mediately follow were meant to give some of the notation of descriptive geometry
in untechnical language for the use of the workmen employed. Let X, Y and Z
be three lines at right angles to each other, and passing through the same point
in space, O, lying at any convenient distance above the floor of the work-shop.

Z

Y¢

Fic. 2. Diagram showing mensural coordinates.

The line X lies North and South; the line Y lies East and West, and the line Z
points to the zenith. Now place the aerodrome on the floor so that its principal
axis lies horizontally in the plane XZ, with its head pointing North, and in such
a position that a line passing through the center of the propellers shall coincide
with the line Y.

When measurements are made on or parallel to the line X, the point of in-
tersection O will be marked 1500 centimetres, and distances toward the South
will be less than, and distances toward the North greater than 1500 centimetres.

When measurements are made on or parallel to the line Z, the point O will
be considered to be marked 2500 centimetres, and distances above will be greater

than, and distances below will be less than 2500 centimetres.

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 15

Lastly, when measurements are made on or parallel to the line Y, the point
O will be marked 3500 centimetres, and distances toward the Kast will be greater
than, and distances toward the West will be less than 3500 centimetres. Meas-
urements in these latter directions will be comparatively infrequent because the

center of gravity and center of pressure both lie in the plane XZ,

EXAMPLE

In the figure the point 7 in the tail, if 15 centimetres to the South of O,
would be graduated 1485 centimetres. A weight (JV) 25 centimetres below the
axis, would be graduated 2475 centimetres. A point 50 centimetres above the
axis would be graduated 2550 centimetres, ete.

CG represents the Center of Gravity of the aerodrome, or (with subseript
letters) of any specially designated part, or with reference to some indicated
condition.

CG, CG. represent the Center of Gravity as referred to the first, or hori-
zontal, and to the second, or vertical plane, respectively.

CP represents the Center of Pressure‘ of the whole aerodrome, or (with a
subseript) of any specially designated part.

CF represents the Center of Figure of the aerodrome, or of any specially
designated part.

Subscripts:

‘‘fw’? refers to the front wings.
‘‘rw’’ refers to the rear wings. ‘¢ 2” refers to the plane XZ.
2 refers to the plane YZ.

“<1” refers to the plane XY.

“>” yvefers to a state of rest. GC Ue

‘6m’ refers to a state of motion.

“‘4’’ represents the total area of the supporting surface; ‘‘ a ’’ represents the

total area of the tail; HP represents the horse-power by Prony brake measure-
ment. ‘‘ Horse-power by formula ’’ is given by Maxim’s formula: *

HP= rev. x diam. of ES aL:

oe

(This formula was not in use at the time of the rubber-motor experiments, for
which the thrust was not taken. It appears to assume that the conditions where
the screws from a fixed position move amass of still air, are the same as those
of free flight. Its results, however, are in better agreement with experiment
than might be anticipated.)

“‘ Flying-weight ’? means everything borne in actual flight, including fuel

and water.

™The aerodrome is sustained by the upward pressure of the air, which must be replaceable by
the resultant pressure at some particular point, designated by CP.

*See Century Magazine, October, 1891.

16 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

EXPERIMENTS witH Axrropromes Nos. 30 anp 31.

Remembering that the principal object of all these experiments is to be able
to predict that setting of the wings and tail with reference to the center of
gravity which will secure horizontal flight, we must understand that in the fol-
lowing tables (see No. 30) the figures CPn=1516.5 em. mean a prediction that
the center of pressure of the sustaining surfaces in motion (CP) is to be found
in a certain position 1516.5; that is, 16.5 em. in advance of the line joining the
propeller shafts. This prediction has been made by means of previous calcula-
tion joined with previous experimental adjustment. We know in a rough way
where the CP will fall on the wings when they are exposed independently if flat,
and at a certain angle, and where it will fall on the tail. From these, we can
find where the resulting CP of the whole sustaining surface will be.

It would seem that when we have obtained the center of gravity by a simple
experiment, we have only to slide the wings or tail forward and back until the
(calenlated) center of pressure falls over this observed center of gravity. But
in the very act of so adjusting the wings and tail, the center of gravity is itself
altered, and the operation has to be several times repeated in order to get the
two values (the center of pressure and center of gravity) as near each other as
they are found in the above-mentioned table, our object being to predict the posi-
tion which will make the actual flight itself horizontal. How far this result has
been obtained, experiment in actual flight alone can show, and from a comparison
of the prediction with the results of observation, we endeavor to improve the
formula.

The difficulties of these long-continued early experiments were enhanced by
the ever-present difficulty which continued through later ones, that it was almost
impossible to build the model light enough to enable it to fly, and at the same
time strong enough to withstand the strains which flight imposed upon it. The
models were broken up by their falls after a few flights, and had to be continu-
ally renewed, while owing to the slightness of their construction, the conditions
of observation could not be exactly repeated; and these flights themselves, as has
already been stated, were so brief in time (usually less than six seconds), so
limited in extent (usually less than twenty metres), and so wholly capricious and
erratic, owing to the nature of the rubber motor and other causes, that very
many experiments were insufficient to eliminate these causes of mal-observation.

It is not necessary to take the reader through many of them, but not to pass
over altogether a labor which was so great in proportion to the results, but whose
results, such as they were, were the foundation of all after knowledge, I will, as
illustrations, take from an almost unlimited mass of such material the observa-
tions of November 20, 1891, which were conducted with Model No. 30 with a
single pair of wings, shown in Plate 1, and with another one, No. 31, also shown

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 1

RUBBER-MOTOR MODEL AERODROMES NOS. 11, 13, 14, 15, 26, 30, 31

bo

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

RUBBER-MOTOR MODEL AERODROMES NOS. 11, 13, 14

SMITHSONIAN -ONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3. PL. 32

NO, 15

RUBBER-MOTOR MODEL AERODROMES NOS. 15, 24

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3

RUBBER-MOTOR MODEL AERODROME NO.

7 No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 17
]
} OBSERVATION OF NOVEMBER 20, 1891.
OpserRveER, 8. P. L. Locauity, Upper HALL, SMITHSONIAN BUILDING.
No. 30. No. 31.
Single wings. Superposed wings.
IME. Boca gdolo HDC DR ORCODR OOOO CORES: Deres 1516.5 em,
(er) ohiaer smoomn ee sreleistolnteletsleteherereicrsiereni 1515 em. 1517 em.
(OU. oh AOd ODS OC AH OO SOOO DER TELE oe | 1528 em. Q
Lengthi(without fender)... 20. .....02 22.06 120 cm. = 3.94 ft. 120 cm. = 8.94 ft.
WiAdEI@ MOR WN SEL PR iarcaraie.0.5, «cue a1, -orcie scene | 120 cm. = 3.94 ft. 120 cm. = 3.94 ft.
; Weight of rubber (72 grammes in each tube)..) 144 gr. = 0.32 Ibs, 144 gr. = 0.32 lbs.
Total flying weight (including tail) ......... 432 gr. = 0.95 lbs. 506 gr. = 1.11 lbs.
TARHSTES GO Bricig (oS 6 POO De RCO Sear |} 380 30
Diameteviof propellers’... s/.. cms ee ene 37 cm. = 1.21 ft. 37em. = |.21 ft.
Wikel UeOLHDNODENLENS pera crajereyciale isis, spe oe acces ers | i em. = 0.23 ft. 7em. = 0.23 ft.
LEC Ni@hs PLO pe MeKs tate lvaicicivcisicfa's sivls= i253 50 cm. = 1.64 ft. 50 cm. = 1.64 ft.
“ 2 ; onesie f Each pair 1954 sq. cm. = 2,13 sq. ft.
Area of wings (each 992 sq.cm.)........... 1984 sq.cm. = 2.13 sq. ft. LTotal 3968 « Sloge
LATOR: OLD eg ged Sod COD BORO OUCOOOU eres 3873 CU = 0.40 573 sq. cm. = 0.40 sq. ft.
Area of wings and tail in No. 30, 2357 sq.cm. = 2.53 sq. ft. 2.53 sq.ft. + .95 = 2.7. Therefore, there

are 2.7 or nearly 3 square feet of sustaining area to the pound.

Results.

Flight. | Aerodrome.
1 | No. 30
2 No. 30
3 No. 31
4 No. 31
5 No. 31
6 No, 31
if No, 30
8 No. 30
9 No. 30

10 No. 30
11 No. 30
12 | No. 30

With 30 turns of the rubber, flew low through 10 metres.

Flew heavily through 12 metres,

Flew high and turned to left; distance not noted.

The right wing having been weighted (to depress it and correct the tendency to turn
fo the left), model flew high, but the rubber ran down when it had obtained a flight

of 10 metres.

The wings were moved backward untilthe CP stood at 1493. The model still turned
to the left: flight lasted three and a-haif seconds; distance not noted.

Vertical tail was adjusted so as to further increase the tendency to go to the right. In
spite of all this, the model turned sharply to the left, flying with a nearly horizontal
motion; time of flight not noted; distance not noted.

Straight horizontal flight; time three and three-fifths seconds, when rubber ran down;
distance 15 metres,

Straight flight as before; time two and four-fifths seconds; distance 13 metres.
With a curved wing in the same position as the flat wing had previously occupied,
mode! flew up and struck the ceiling (nearly 30 feet high), turning to right, with a

flight whose curtate length was 10 metres.

Wing having been carried back 5 centimetres, model still flew up, but not so high, and
still turned to the right.

Wings carried back 5 centimetres more; model still flew high; time two and two-fifths
seconds; distance 13 metres.

Wings carried back 4 centimetres more; model still flew high during a flight of 13 metres.

The observations now ceased, owing to the breaking up of the model.

we

18 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27
in Plate 1, with superposed wings, which was used for the purpose of compari-
son. S. P. Langley was the observer, the place of observation the larger upper
hall of the Smithsonian building, at Washington, the time being taken by a stop-
watch, and the distance by a scale laid down upon the floor. The models were in
every case held by an assistant and launched by hand, being thrown off with a
slight initial velocity. In the case of No. 30, the preliminary calculation of the
position of the center of pressure had been made by the process already de-
scribed; the center of gravity, with reference to the horizontal plane, was deter-
mined by simply suspending the whole by a cord.

The objects of these experiments, as of every other, were to find the practi-
cal conditions of equilibrium and of horizontal flight, and to compare the caleu-
lated with the observed positions of the center of pressure. They enable us to
make a comparison of the performances given by earlier ones with a light rub-
ber motor, with the relatively heavy motors used to-day, as well as a comparison
of single flat, single curved, and superposed flat wings.

The average time of the running down of the rubber in flight was something
like three seconds, while the average time of its running down when standing
still was but one and a half seconds. It might have been expected from theory
that it would take longer to run down when stationary, than in flight, and this
was one of the many anomalies observed, whose explanation was found later in
the inevitable defects of such apparatus.

The immediate inferences from the day’s work were:

1. That the calculated position of the CP at rest, as related to the CG, is
trustworthy only in the case of the plane wing.

2. The formula altogether failed with the curved wing, for which the CP
had to be carried indefinitely further backward.

On comparing the previous flights of November 14, with these, it seems that
with the old rubber motor of 35 grammes and 50 turns, the single wing, either
plane or curved, is altogether inferior to the double wing; while with the in-
creased motor power of this day, the single wing, whether plane or curved, seems
to be as good as the double wing. It also seems that the curved wing was rather
more efficient than the plane one.

The weight of the rubber in each tube was 72 grammes, or 0.16 pounds ; mean
speed of flight in horizontal distance 4} metres (about 15 feet) per second.*

From experiments already referred to, there were found available 300 foot-
pounds of energy in a pound of rubber as employed, and in 0.16 of a pound, 48

8 :
foot-pounds of energy were used; 300 or 0.00145=the horse-power exerted in
Oe ,

° Subsequent observations indicate that the maximum velocity of horizontal flight must have been
about 10 metres per second.

= Kim

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 19

one minute, but as the power was in fact expended in 1/20 of that time we have
20 x 0.00145=0.029; that is, during the brief flight, about 0.03 of a horse-power
was exerted, and this sustained a total weight of only about a pound.

In comparing this flight with the ideal conditions of horizontal flight in ‘‘Ae-

”? it will be remembered that this model’s flight was so irregular and

rodynamics,
so far from horizontal, that in one case it flew up and struck the lofty ceiling.
The angle with the horizon is, of course, so variable as to be practically un-
known, and therefore no direct comparison can be instituted with the data given
on page 107 of ‘‘ Experiments in Aerodynamics,’’ but we find from these that at
the lowest speed there given of about 35 feet per second, 0.03 of a horse-power
exerted for three seconds would carry nearly one pound through a distance of
somewhat over 100 feet in horizontal flight.

The number of turns of the propellers multiplied by the pitch corresponds
to a flight of about 16 metres, while the mean actual flight was about 12. It is
probable, however, that there was really more slip than this part of the obser-
vation would indicate. It was also observed that there seemed to be very little
additional compensatory gain in the steering of No. 30 for the weight of the long
rudder-tail it carried. It may be remarked that in subsequent observations the
superiority of the curved wing in lifting power was confirmed, though it was
found more liable to accident than the flatter one, tending to turn the model over
unless it was very carefully adjusted.

It may also be observed that these and subsequent observations show, as
might have been anticipated, that as the motor power increased, the necessary
wing surface diminished, but that it was in general an easier and more efficient
employment of power to carry a surface of four feet sustaining area to the
pound than one of three, while one of two feet to the pound was nearly the limit
that could be used with the rubber motor.’®

It may be remarked that the flights this day, reckoned in horizontal dis-
tance, were exceptionally short, but that the best flights at other times obtained
with these models (30 and 31) did not exceed 25 metres. Such observations were
continued in hundreds of trials, without any much more conclusive results.

” Observers following de Lucy have long since called attention to the fact that as the scale of
Nature's flying things increases, the size of the sustaining surfaces diminishes relatively to the weight
EE is sur-
8 weight
prisingly constant when bats varying in weight as much as 250 times are the subject of experiment,
and later observations by Marey have not materially affected the statement. As to the muscular power
which Nature has imparted with the greater or lesser weight, this varies, decreasing very rapidly as
the weight increases. The same remark may be made, apparently with at least approximate truth,
with regard to the soaring bird, and the important inference is that if there be any analogy between
the bird and the aerodrome, as the scale of the construction of the latter increases, it may be reason-
ably anticipated that the size of the sustaining surfaces will relatively diminish rather than increase.

We may conveniently use M. Harting's formula in the form a=n?wi= ¥ where a=area in sq.
cm., w the weight in grammes, 7 the length of the wing in cm., n and m constants derived from
observation.

sustained. M. Harting (Aeronautical Society, 1870) has shown that the relation

20 SMITHSONIAN CONTRIBUTIONS LO KNOWLEDGE vou. 27

The final results, then, of the observations with rubber-driven models (which
were commenced as early as 1887, continued actively through the greater por-
tion of the year 1891 and resumed, as will be seen later, even as late as 1895),
were not such as to give information proportioned to their trouble and cost, and
it was decided to commence experiments with a steam-driven aerodrome on a
large scale.

CHAPTER III
AVAILABLE MOTORS

In the introductory chapter to ‘‘ Experiments in Aerodynamics,”’ it was
asserted that

*“ These researches have led to the result that mechanical sustentation of
heavy bodies in the air, combined with very great speeds, is not only possible,
but within the reach of mechanical means we actually possess.”’

It was, however, necessary to make a proper selection in order to secure
that source of power which is best adapted to the requirements of mechanical
flight. Pénaud had used india rubber as the cheapest and at the same time the
most available motor for the toys with which he was experimenting, but when
models were constructed that were heavier than anything made prior to 1887, it
appeared, after the exhaustive trials with rubber referred to in the preceding
chapter, that something which could give longer and steadier flights must be
used as a motor, even for the preliminary trials, and the construction of the
large steam-driven model known as No. 0, and elsewhere described, was begun.
Kven before the completion of this, the probability of its failure grew so strong
that experiments were commenced with other motors, which it was hoped might
be consistent with a lighter construction.

These experiments which commenced in the spring of 1892 and continued
for nearly a twelvemonth, were made upon the use of compressed air, carbonic-
acid gas, electricity in primary and storage batteries, and numerous other con-
trivances, with the result that the steam engine was finally returned to, as be-
ing the only one that gave any promise of immediate success in supporting a
machine which would teach the conditions of flight by actual trial, though it may
be added that the gas engine which was not tried at this time on account of
engineering difficulties, was regarded from the first as being the best in theory
and likely to be ultimately resorted to. All others were fundamentally too
heavy, and weight was always the greatest enemy.

It is the purpose of this chapter to pass in brief review the work that was

done and the amount of energy that was obtained with these several types of
motors, as well as the obstacles which they presented to practical application
upon working aerodromes.

Inp1a Russer

India rubber is the source of power to which the designer of a working
model naturally turns, where it is desirable that it shall be, above all, light and
free from the necessity of using complicated mechanism. Rubber motors were,

21

22 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vob. 27

therefore, used on all of the earlier models, and served as the basis of calcula-
tions made to determine the amount of power that would be required to propel
aerodromes with other sources of energy.

Some of the disadvantages inherent in the use of rubber are at once appar-
ent, such as the limited time during which its action is available, the small total
amount of power, and the variability in the amount of power put forth im a
unit of time between the moment of release and the exhaustion of the power. In
addition, serious, though less obvious difficulties, present themselves in practice.

There are two ways in which rubber can be used; one by twisting a hank of
strands, and, while one end is held fast, allowing the other to revolve; the other,
by a direct longitudinal stretching of the rubber, one end being held fast and the
other attached to the moving parts of the mechanism. The former method was
adopted by Pénaud, and was also used in all of my early constructions, but while
it is most convenient and simple in its (theoretical) application, it has, in addi-
tion to the above drawbacks, that of knotting or kinking, when wound too many
turns, in such a way as to cause friction on any containing tube not made im-
practicably large, and also that of unwinding so irregularly as to make the result
of one experiment useless for comparison with another.

In 1895, some experiments were made in which the latter method was used,
but this was found to involve an almost impracticable weight, because of the
frame (which must be strong enough to withstand the end pull of the rubber)
and the mechanism needed to convert the pull into a movement of rotation,

As the power put forth in a unit of time varies, so there is a correspond-
ing variation according to the original tension to which the rubber is subjected.
Thus in some experiments made in 1889 with a six-bladed propeller 18.8 inches
in diameter, driven by a rubber spring 1.3 inches wide, 0.12 inch thick and 3 feet
long, doubled, and weighing 0.38 pound, the following results were obtained:

Number of twists of rubber........ 59 75 100
Time required to run down......... 7 sec. 10 sec. 12 sec.
Foot-pounds developed ..........-. 37.5 63.0 124.6
Foot-pounds developed per min..... 321.4 378.0 623.0
Horse-power developed ...........- 0.0097 0.0115 0.0189

Thus we see that, with twice the number of turns, more than three times the
’

amount of work was done and almost twice the amount of power developed, giv-

ine as a maximum for this particular instance 328 foot-pounds per pound of
rubber.

The usual method of employing the twisted rubber was to use a number of

fine strands formed into a hank looped at each end. One of these hanks, con-

b

sisting of 162 single or 81 double strands of rubber, and weighing 73 grammes

? S z : ’

when given 51 turns developed 55 foot-pounds of work, which was put out in 4

seconds. This corresponds to 0.01 horse-power per minute for one pound of

rubber.

—— = = gay

el, ee

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT a0

The results of a large number of tests show that one pound of twisted rub-
ber can put forth from 450 to 500 or more foot-pounds of work, but at the cost
of an overstrain, and that a safe working factor can hardly be taken at higher

? of the rubber, which

than 300 foot-pounds, if we are to avoid the ‘‘ fatigue ’
otherwise becomes as marked as that of a human muscle.

While twisting is an exceedingly convenient form of application of the re-
silience of rubber to the turning of propelling wheels, the direct stretch is, as
has been remarked, much more efficient in foot-pounds of energy developed by
the same weight of rubber. It was found that rubber could not, without undue
‘< fatigue,’’ be stretched to more than four and a half times its original length,
though experiments were made to determine the amount of work that a rubber
band, weighing one pound, was capable of doing, the stretching being carried
to seven times its original length. The results varied with the rubber used and
the conditions of temperature under which the experiments were tried, ranging
from 1543 foot-pounds to 2600 foot-pounds. The tests led to the conclusion that,
for average working, one pound of rubber so stretched, is capable of doing 2000
foot-pounds of work, but, owing to the weight of the supporting frame and of
the mechanism, this result can be obtained only under conditions impracticable
for a flying machine. In the more practicable twisted form it furnishes, as has
been said, less than a fifth of that amount.

The conclusions reached from these experiments are:

1. The length of the unstretched rubber remaining the same, the sustaining
power will be directiy proportional to the weight of rubber;

2. With a given weight of rubber, the end strain is inversely proportional
to the length of the unstretched rubber ;

3. With a given weight of rubber, the work done is constant, whatever the
form; hence if we let w=the work in foot-pounds, g=the weight of the rubber
in pounds, and k=a constant taken at 2000 as given above, we have

w=kg=2000 g foot-pounds.

This is for an extension of seven units of length, so that for a unit of extension

we would have approximately
w=300 g foot-pounds

which for four units of extension corresponds very closely to the 1300 foot-pounds
which Pénaud claims to have obtained.
4. The end strain varies with the cross-section for a given unit of extension.
These results can lead to but one conclusion; that for the development of the
same amount of power when that amount shall be 1 horse-power or more, rub-
ber weighs enormously more than a steam engine, besides being less reliable

24 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

for a sustained effort, and, therefore, cannot be used for propelling aerodromes
intended for a flight that is to be prolonged beyond a few seconds.’

It may be desirable to present a tabular view of the theoretical energy of
available motors, which it will be noticed is a wholly different thing from the
results obtained in practice. Thus, we represent the weight of rubber only, with-
out regard to the weight of the frame required to hold it. In the steam engine,
we conskler the theoretical efficiency per pound of fuel, without regarding the
enormous waste of weight in water in such small engines as these, or the weight
of the engine itself. We treat the hot-water engine in like manner, and in re-
gard to carbonic acid and compressed air, we take no note of the weight of the
containing vessel, or of the cylinders and moving parts. In the same way we
have the theoretical potency of electricity in primary and storage batteries,
without counting the weight of the necessary electromotors; and of the inertia-
engine without discussing that of the mechanism needed to transmit its power.

Foot-pounds of energy in one pound of

PASOLING aa fo onl fete Sra ava sua shus dey alm Blake etorele soins Nae SI OEE EE eee 15,625,280
yA) 10) Mee ah Oia ert cia ci cic no oa doo SonoSte MGs ac 9,721,806
AUB POW GOT o.o's ssc iecevore ve ies ea te Pes area es Rate one Te ete 960,000
Hot water, under pressure of 100 atmospheres...................6-. 383,712
Air, under pressure of 100 atmospheres, isothermal expansion....... 120,584
Liquid carbonic acid, at temperature of 30° and pressure of 100
atmospheres: £2.filxcte fence teres oe pee ee enn eee 78,800
Electric battery; short-lived, thin walled; chromic acid and platinum. 75,000
Steel ring, 8 inches in diameter, at speed of 3000 turns per minute. . 19,000
Storage: battery: +. 2>.s..6 cts. cS nen eee le ee ee eee 17,560
Rubbers pulled scotacweys tape tenet ore Cn eee 2,000
Rubbers twisted! \5al.se sorcerer ee Ee ee 300

It may be interesting to consider next, in even a roughly approximate way,
what may be expected from these various sources of energy in practice.

Stream ENGINE

The steam engine on a small scale, and under the actual restrictions of the
model, must necessarily be extremely wasteful of power. If we suppose it to
realize 2 per cent of the theoretical energy contained in the fuel, we shall be as-
suming more than was actually obtained. The energy of the fuel cannot be
obtained at all, of course, without boiler and engine, whose weight, for the pur-
pose of the following calculation, must be added to that of the fuel; and if we
suppose the weight of the boilers, engines and water, for a single minute’s flight,
to be collectively ten pounds, we shall take an optimistic view of what may be
expected under ordinary conditions. We have in this view 1/500 of the theo-

*A singular fact connected with the stretching of rubber is that the extension is not only not
directly proportional to the power producing it, but that up to a certain limit it increases more
rapidly than the power, and after this the relation becomes for a time more nearly constant, and
after this again the extension becomes less and less in proportion.

In other words, if a curve be constructed whose abscissae represent extensions, and ordinates the

corresponding weights, it will show a reverse curvature, one portion being concave toward the axis
of abscissae, the other convex.

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MITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 7

RUBBER-PULL

FRONT ELEV

PHOTOGRAPHED J

RUBBER-PULL MODEL AERODROME

7
:
.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 8

RUBBER-PULL AERG¢

SIDE ELEVAT

PHOTOGRAPHED

RUBBER-PULL MODEL AERODROME

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 25

retical capacity possibly realizable under such conditions, but if we take 1/1000
we shall probably be nearer the mark. Even in this case we have, when using
gasoline as fuel, 15,625 foot-pounds per minute, or nearly 0.50 horse-power, as
against .0091 horse-power in the case of the rubber, so that even with this waste
and with the weight of the engines necessary for a single minute’s service, the
unit weight of fuel employed in the steam engine gives 55 times the result we
get with rubber.

With aleohol we have about 3 the result that is furnished by gasoline, since
nearly the same boiler and engine will be used in either case. Certain difficulties
which at first appeared to be attendant on the use of gasoline on a small seale
induced me to make the initial experiments with aleohol. This was continued
because of its convenience during a considerable time, but it was finally displaced
in favor of gasoline, not so much on account of the superior theoretical efficiency
of the latter, as for certain practical advantages, such as its maintaining its flame
while exposed to wind, and like considerations.

GUNPOWDER

Although there are other explosives possessing a much greater energy in
proportion to their weight than gunpowder, this is the only one which could be
considered in relation to the present work, and the conclusion was finally reached
that it involved so great a weight in the containing apparatus and so much ex-
periment, that, although the simplicity of its action is in its favor where crude
means are necessary, experiments with it had better be deferred until other
things had been tried.

Hor-Water ENGINE

A great deal of attention was given to the hot-water engine, but it was
never put to practical use in the construction of an aerodrome, partly on account
of the necessary weight of a sufficiently strong containing vessel.

Compressep AIR

Compressed air, like the other possible sources of power, was investigated,
but caleulations from well-authenticated data showed that this system of pro-
pelling engines would probably be inadequate to sustain even the models in long
flights. As the chief difficulty lies in the weight, not of the air, but of the con-
taining vessel, numerous experiments were made in the construction of one at
once strong and light. The best result obtained was with a steel tube 40 mm.
in diameter, 428 mm. in length, closed at the ends by heads united by wires,
which safely contained 538 eubie em. of air at an initial pressure of 100 atmos-
pheres for a weight of 521 grammes.

26 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. Hl

If we suppose this to be used, by means of a proper reducing valve, at a
mean pressure of 100 pounds, for such an engine as that of Aerodrome No. 5,
which takes 60 cubic em. of air at each stroke, we find that (if we take no account
of the loss by expansion) we have 18,329 foot-pounds of energy available, which
on the engine described will give 302 revolutions of the propellers.

There are such limits of weight, and the engines must be driven at such high
speeds, that the increased economy that might be obtained by re-heating the
air would be out of the question. The principal object in using it would have
been the avoidance of fire upon the aerodrome, and the expansion of the unheated
air would probably have caused trouble with freezing, while the use of hot (1. e.
superheated) water was impracticable. So when, after a careful computation, it
was found that, having regard to the weight of the containing vessel, only enough
compressed air could be stored at 72 atmospheres and used at 4, to run a pair
of engines with cylinders 0.9 inch in diameter by 1.6 inches stroke, at a speed of
1200 revolutions per minute for 20 seconds, all further consideration of its adap-
tation to the immediate purpose was definitely abandoned. This course, how-
ever, was not taken until after a model aerodrome for using compressed air had
been designed and partially built. Then, after due consideration, it was decided

to make the test with carbonic-acid gas instead.

Gas

The gas engine possesses great theoretical advantages. At the time of these
experiments, the gas engine most available for the special purposes of the models
was one driven by air drawn through gasoline. As the builders could not agree
to reduce the weight of a one horse-power engine more than one-half of the then
usual model, and as the weight of the standard engine was 470 pounds, it was
obvious that to reduce this weight to the limit of less than 3 pounds was im-
practicable under the existing conditions, and all consideration of the use of gas

vas abandoned provisionally, although a gasoline engine of elementary simplic-
ity was designed but never built. I purposed, however, to return to this at-
tractive form of power if I were ever able to realize its theoretical advantages

on the larger seale which would be desirable.

KLECTRICITY

As it was not intended to build the model aerodromes for a long flight, it
was thought that the electric motor driven by a primary or storage battery might
possibly be utilized. It therefore occurred to me that a battery might be con-
structed to give great power in proportion to its weight on condition of being
short-lived, and that in this form a battery might perhaps advantageously take
the place of the dangerous compressed-air tubes that were at the time (1893)

pail

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT a

under consideration for driving the models. I assumed that the longest flight of
the model would be less than five minutes. Any weight of battery, then, that the
model carried in consumable parts lasting beyond this five minutes would be
lost, and hence it was proposed to build a battery, the whole active life of which
would be comprised in this time, to actuate a motor or motors driving one or
two propellers.

According to Daniell, when energy is stored in secondary batteries, over
300,000 megergs per kilogramme of weight can be recovered and utilized if
freshly charged.

300,000 megerg's=0.696 lLorse-power for 1 min.
300,000 megerg's =0.139 horse-power for 5 min.

In a zine and copper primary battery with sulphurie acid and water, one
kilogramme of zine, oxidized, furnishes at least 1200 calories as against 8000
for one kilogramme of carbon, but it is stated that the zine energy comes in so
much more utilizable a form that the zine, weight for weight, gives practically,
that is in work, 40 per cent that of carbon. The kilogramme of carbon gives
about 8000 heat units, each equal to 107 kilogrammetres, or about 6,176,000 foot-
pounds. Of this, in light engines, from 5 to 10 per cent, or at least 308,800
foot-pounds, is utilized, and 2 of this, or about 124,000 foot-pounds, would seem
to be what the kilogramme of zine would give in actual work. But to form the
battery, we must have a larger weight of fluid than of zinc. and something must
be allowed for copper. If we suppose these to bring the weight up to 1 kilo-
gramme, we might still hope to have 50,000 foot-pounds or 1.5 horse-power for
one minute, or 0.3 horse-power for 5 minutes.

Storage batteries were offered with a capacity of .25 horse-power for 5 min-
utes per kilogramme, but according to Daniell one cannot expect to get more
than 0.139 horse-power from a freshly charged battery of that weight for the
same time.

The plan of constructing a battery of a long roll of extremely thin zine or
magnesium, winding it up with a narrower roll of copper or platinized silver, in-
sulating the two metals and then pouring over enough acid to consume the major
portion of the zine in 5 minutes, was carefully considered, but the difficulties were
so discouraging, that the work was not undertaken.

The lightest motors of 1 horse-power capacity of which any trace could be
found weighed 25 pounds, and a prominent electrician stated that he would not
attempt to construct one of that weight.

In trials with a $ horse-power motor driving an 80 em. propeller of 1.00
pitch-ratio, I apparently obtained a development of 0.56 indicated horse-power
at 1265 revolutions; but at lower speeds when tried with the Prony brake, the
brake horse-power fell to 0.10 at 546 revolutions, and even at 1650 revolutions

28 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

it was but 0.262 indicated, with a brake horse-power of 0.144, or 55 per cent of
that indicated.

With these results both of theoretical caleulation and practical experiment,
all thought of propelling the proposed aerodrome by electricity was necessarily

abandoned.

Carsonic-Acip Gas

At the first inception of the idea, it seemed that carbonic-acid gas would
be the motive power best adapted for short flights. It can be obtaimed in the
liquid form, is compact, gives off the gas at a uniform pressure dependent upon
the temperature, and can be used in the ordinary steam engine without any
essential modifications. The only provision that it seemed, in advance, neces-
sary to make, was that of some sort of a heater between the reservoir of liquid
and the engine, in order to prevent freezing, unless the liquid itself could be
heated previous to launching.

The engines in which it was first intended to use carbonic acid were the little
oscillating cylinder engines belonging to Aerodrome No. 1. The capacity of
each cylinder was 21.2 eu. em., so that 84.8 cu. em. of gas would be required to
turn the propellers one revolution when admitted for the full stroke, and 101,760
eubie em. for 1200 revolutions. The density of the liquid at a temperature of
24° C. was taken as .72, and as 1 volume of liquid gives 180 volumes of gas at

a pressure of 24 atmospheres, we have se ees eu. em. of liquid, or 407

grammes required for 1200 revolutions of the engines.

Thus, a theoretical calculation seemed to indicate that a kilogramme of
liquid carbonic acid would be an ample supply for a run of two minutes. The
experiments were, at first, somewhat encouraging. The speed and apparent
power of the engines were sufficient for the purpose, but the length of time
during which power could be obtained was limited.

In 1892, 415 grammes of carbonic acid drove the engines of Aerodrome No.
3 700 revolutions in 60 seconds, 900 in 75, and 1000 in 85 seconds, at the end of
which time the gas was entirely expended. The diameter of these cylinders was
2.4 em., the stroke of the pistons 7 em., and the work done, that of driving a pair
of 50 em. propellers, when taken in comparison with the propeller tests detailed
elsewhere, amounted to an effective horse-power of about 0.10 for the output of
the engine.

The difficulties, however, that were experienced were those partially fore-
seen. The expansion of the gas made such serious inroads upon the latent heat
of the liquid, that lumps of solid acid were formed in the reservoir, and could be
heard rattling against the sides when the latter was shaken, while the expansion
of the exhaust caused such a lowering of temperature at that point, that the

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 929

pipes were soon covered with a thick layer of ice, and the free exit of the escap-
ing gas was prevented.

Such difficulties are to be expected with this material, but here they were
enhanced by the small scale of the construction and the constant demand for
lightness. And it was found to be very hard to fill the small reservoirs intended
to carry the supply for the engines. When they were screwed to the large case
in which the liquid was received and the whole inverted, the small reservoir
would be filled from one-third to one-half full, and nothing that could be done
would force any more liquid to enter.

In view of these difficulties, and the objections to using a heater of any sort
for the gas, as well as the absolute lack of success attendant upon the experi
ments of others who were attempting to use liquid CO, as a motive power on a
large scale elsewhere, experiments were at first temporarily and afterwards
permanently abandoned.

The above experiments extended over nearly a year in time, chiefly during
1892, and involved the construction and use of the small aerodromes Nos. 1, 2,

and 3, presently described.

CHAPTER IV
EARLY STEAM MOTORS AND OTHER MODELS

In dealing with the development of the aerodrome, subsequent to the early
rubber-driven models, the very considerable work done and the failures incurred
with other types of motors than steam, have been briefly dealt with in the pre-
ceding chapter, but are scarcely mentioned here, as no attempts at long flights
were ever successful with any other motor than steam, and no information was
gained from any of the experiments made with compressed air, gas, carbonic
acid, or electricity, that was of much value in the development of the successful
steam machines.

In November, 1891, after the long and unsatisfactory experiments with rub-
ber-driven models already referred to, and before most of the experiments with
other available motors than steam had been made, I commenced the construction
of the engines and the design of the hull of a steam-driven aerodrome, which
was intended to supplement the experiments given in ‘‘ Aerodynamics ’’ by
others made under the conditions of actual flight.

In designing this first aerodrome, here called No. 0, there was no precedent
or example, and except for the purely theoretical conditions ascertained by the
experiments described in ‘¢ Aerodynamics,’’ everything was unknown. Next to
nothing was known as to the size or form, as to the requisite strength, or as to the
way of attaching the sustaining surfaces; almost nothing was known as to the
weight permissible, and nothing as to the proper seale on which to build the ae-
rodrome, even if the design had been obtained, while everything which related
to the actual construction of boiler and engines working under such unprece-
dented conditions was yet to be determined by experiment.

The seale of the actual construction was adopted under the belief that it
must be large enough to carry certain automatic steering apparatus which I had
designed, and which possessed considerable weight. I decided that a flying ma-
chine if not large enough to carry a manager, should in the absence of a human
directing intelligence, have some sort of automatic substitute for it, and be large
enough to have the means of maintaining a long and steady flight, during which
the problems (which the rubber-driven models so imperfectly answered) could
be effectually solved.

When, in 1891, it was decided to attempt to build this steam aerodrome, the
only engine that had been made up to that time with any claim to the lightness
and power I was seeking, was the Stringfellow engine, exhibited at the Crystal
Palace in London, in 1868, which it was then announced developed 1 horse-

2
o

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 31

power for a total weight (boiler and engines) of 13 pounds. The original engine
came into the possession of the Institution in 1889 as an historical curiosity, but
on examination, it was at once evident that it never had developed, and never
could develop the power that had been attributed to it, and probably not one-
tenth so much.

With the results obtained on the whirling-table at Allegheny as a basis, a
theoretical computation of the weight which 1 horse-power would cause to soar
showed that, with a plane whose efficiency should be equal to that of a 30x48
inch plane set at an angle of 5° and moving at a speed of 54 miles an hour, 1
horse-power would support 120 pounds.’ With a smaller angle even better results
could be obtained, but as the difficulties of guidance increase as the angle di-
minishes, I did not venture to aim at less than this. In this computation, no
allowance was made for the fact that these results were obtained by a mechanism
which forcibly maintained the supporting surface in the ideal condition of the
best attainable angle of attack as if in perfect equilibrium, and above all in the
equally ideal condition of perfectly horizontal flight.

Besides this, I had to consider in actual flight the air resistance due to the
guy wires and hull, but after making an allowance of as much as three-quarters
for these differences between the conditions of experiment and those of free
flight, I hoped that 1 horse-power would serve to carry 30 pounds through the
air if a supporting surface as large as 3 feet to the pound could be provided,
and this was the basis of the construction which I will now deseribe.

The general form of this Aerodrome No. 0, without wings or propellers,
is shown in the accompanying photograph in Plate 10. Its dimensions and its
weights, as first designed, and as finally found necessary, are as follows:

COMPARISON OF ESTIMATED AND ACTUAL WEIGHTS OF PARTS OF
AERODROME “0O”—IN POUNDS AND OUNCES.

Estimated Actual
lbs. OZ. lbs. OZ.

lDHEHAGE “hs dec dan scasvonbd BOuODOODOne AO Oop COnON UDIUeCOMOGOS 4 0 4 1
IB OLLCLS TANG UENO S crete oe fern. ciel orsie iol faliele viene) eke (a fe" alatasaoeleve= oe 'e jas 8 11 13 14
Pinips ange Atta chm Cn tsearicel tir y-isveis)atetel-peieiam eraercieheror>) sfeteialet sls 0 0 1 10
Steenimese Ap DATAUUSH er clevatsrersteeditekote rere caer cl et ou seperet erakele a (one! eel) ai 0 6 0 0
Frame of Hull and Braces, including bowsprit and tail tube. . ti 7 8 11
Oiletantkecoverineean dupipesssrciscccmicisecioescite ns celts) valor 0 0 0 13
Shafts, ball bearings (2:1) and wooden propellers (1:7) .... 1 14 3 8
Wines (asd) ane ety Sar (OG))ctepertesckesoreheysuslerelelelaleisleleleleleyelel«a/aJo > 4 0 5 13
SAN = cep HHO GakD Oba bh DDC eo SU DUO crn ate aie » ocmomacr or 1 5 2 2
ARC e Ain) he spopeeennonpdosaccadde -apaeonesomob OUDOnTOD 9 0 4 0
IL OEH WENO OL TOF WiatOTates clere crcleteleecleloicieinelaistele' aici 27 11 44 8

(The weights attained in the actual making were, as is seen, nearly double those
first estimated, and this constant increase of weight under the exigencies of con-
struction was a feature which could never be wholly eliminated.)

+See footnote on page 32.

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32 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

After studying various forms for the hull or body of the prospective aero-
drome, £ was led to adopt the lines which Nature has used in the mackerel as
most advantageous so far as the resistance of the air was concerned, but it proved
to be difficult in construction to make the lines of the bow materially different
from those of the stern, and in this first model the figure was symmetrical
throughout.

As I wish that my experience may be of benefit to the reader, even in its
failures, L will add that I made the not unnatural mistake of building on the plan
on which the hull of an ordinary ship is constructed; that is, making the hull
support the projecting bowsprit and other parts. In the aerodrome, what cor-
responds to the bowsprit must project far in advance of the hull to sustain the
front wings, and a like piece must project behind it to sustain the rear wings and
the tail, or the supporting surfaces of whatever kind. The mistake of the con-
struction lay in disjoining these two and connecting them indirectly by the in
sufficiently strong hull which supported them. This hull was formed of longi-
tudinal U-shaped ribs of thin steel, which rested on rings made of an alloy of
aluminum, which possessed the lightness of the latter metal with very consider-
able toughness, but which was finally unsatisfactory. I may say parenthetically
that in none of the subsequent constructions has the lightness of aluminum been
found to compensate for its very many disadvantages. The two rods, which were
each 1 metre in length, were with difficulty kept rigorously in line, owing to the
yielding of the constructionally weak hull. It would have been better, in fact, to
have carried the rod straight through at any inconvenience to the disposition of
the boilers and the engine. :

I may add that the sustaining surfaces, which were to be nearly flat wings,
composed of silk stretched from a steel tube with wooden attachments, were to

1The following table taken from ‘‘Experiments in Aerodynamics,” p. 107, gives the data for soaring of
30x 4.8 inch planes, weight 500 grammes.

Weight with planes
of like form that

Aaeste Scie! speed Work aac 1 horse-power will
with . Per ee. drive through the air
horizon at velocity V.
a. F i (ees
Metres Feet Kilogram- | Foot- ~ Kilo. P
ounds.
per second. | per second. metres. pounds. | grammes.
: | lo
45° 11.2 36.7 a6 2,434 6.8 15
350 10.6 34.8 17 | 11268 15.0 29
15 Ng hoy’ 36.7 86 625 26.5 58
10 12.4 40.7 65 | 474 34.8 77
5 15.2 49.8 41 297 Tso || 122
2 20.0 65.6 24 174 95.0 209

The relations shown in the above table hold true only in case of planes supporting about 1.1 pounds to each
square foot of sustaining area. Fora different proportion of area to weight, other conditions would obtain.

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 33

have been carried on the front rod, but, as subsequent experience has shown,
these wings would have been inadequate to the work, both from their insuffi-
cient size and their lack of rigidity.

The propellers, which were to be 80 em. in diameter, 1.25 pitch-ratio, and
which were expected to make from five to six hundred revolutions a minute, were
carried on the end of long tubular shafts, not parallel, but making with each
other an angle of 25 degrees, and united by gears near the bow of the vessel in
the manner shown in Plate 10.

The first engines were of the oscillating type, with the piston-rod connected
directly to the crank; were very light, and were unprovided with many of the
usual fittings belonging to a steam engine, such as rod or piston packing; and
their construction was crude in comparison with their successors. They were
tested with the Prony brake and found to be deficient in power, for with a steam
pressure of 80 pounds to the square inch, they ran at the rate of 1170 revolu-
tions per minute, and developed only .363 horse-power. It soon became evident
that they were too light for the work that it was intended that they should do,
and steps were taken, even before the completion of these tests, for the construc-
tion of a pair of more powerful cylinders, which should also be provided with a
special boiler for the generation of the steam. Acting upon the supposition,
which, as the sequel showed, was unwarranted, that compounding would result
in a saving of steam, it was decided to work with compounded cylinders. As two
propellers were to be used, they were each fitted with a distinct pair of cylinders
working directly upon the shaft, but so connected by gearing that they were
compelled to turn at the same rate of speed.

The cylinders were of the inverted oscillating type, like the first pair of
engines, but, unlike them, they were single-acting. The dimensions were: di-
ameter of high-pressure cylinder 1.25 inches; low pressure, 1.94 inches, with a
common stroke of 2 inches, and with cranks set opposite to each other so that
one cylinder was always at work. The cylinders were held at their upper ends
by a strap passing around a hollow conical trunk, which served the double pur-
pose of a support for the cylinders and an intermediate receiver between them.
This receiver had a mean inside diameter of 1.25 inches, with a length of 4.75
inches, so that it had about twice the cubical capacity of the high-pressure cyl-
inder, while the displacement of the low-pressure cylinder was about 2.5 times
that of the high; ratios that would have given satisfactory results, perhaps, had
the steam pressure and other conditions been favorable to the use of the com-
pound principle in this place. There were no valves for the admission of the
steam, for, inasmuch as the engines were single-acting, it was possible to make
ports in the eylinder-head act as the admission and exhaust ports as the cylinder
oscillated, and thus avoid the complication and weight of eccentric and valves.

4

34 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

These cylinders were set in a light frame at an angle of 25° with each
other, or 12.5° with the median line of the aerodrome, and drove the long pro-
peller shafts as shown in Plate 10, No.0. At the extreme forward end of the
crank-shafts there was a pair of intermeshing bevel gears which served to main-
tain the rate of revolution of the two propellers the same.

The boiler built for this work was a beehive-shaped arrangement of coils
of pipe. It consisted at first, as shown in Fig. 3, of three double coils of 2-inch
copper pipe coiled up in the shape of a truncated cone, carrying in the central
portion a pear-shaped receiver into the upper portion of which the water cir-

Fic. 3. Boilers in use in 1891-1892.

culating through the coils discharged. Hach of these receivers was connected
at the top with the bottom of a long cylindrical drum, with hemispherical ends,
which formed a steam space from which the supply for the engines was drawn.
The lower ends of the coils were connected with an injection pipe supplying the
water. Hach ‘‘ beehive ’’ had 23 turns of tubing, and had a base of 7.5 inches
and a top diameter of 6 inches, the steam drum being 2.5 inches in diameter. I
may here say that in the selection of the general type of boiler for the work to
be done, there was never any hesitation regarding the use of the water-tube
variety. Their superiority for the quick generation of large volumes of steam
had been so pronounced that nothing else seemed capable of competing with

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 35

them in this respect, regardless of the absolute economy of fuel that might or
might not be exhibited. Hence, to the end of my experiments nothing else was
used.

Even before the ‘‘beehive’’ boiler was completed, I was anxious to ascertain
what could be done with a coil of pipe with a stream of water circulating through
it, as well as with various forms of burners, for I realized that the success of the
apparatus depended not only upon getting an exceedingly effective heating sur-
face, but also an equally effective flame to do the heating.

For fuel I naturally turned to the liquids as being more compact and readily
regulated. Whether to use some of the more volatile hydrocarbons or alcohol,
was still an unsolved problem, but my opinion at the time was that, on the lim-
ited scale of the model, better results could probably be obtained with alcohol.

In the experiments made with a coil preliminary to the trial of the ‘‘ bee-
hive ’’ boiler, I tried a simple horizontal coil of 23-inch copper pipe into which
two forked burners working on the Bunsen principle and using eity illuminating
gas, were thrust. The jets were about $ inch apart. The arrangement primed
so badly that the engines could not get rid of the entrained water, and would only
make a few turns.

I then tried the same coil with two 1.25-inch drums in the inside and with
five longitudinal water tubes at the bottom, beneath which were the same two
forked burners used in the previous experiment. The coils were covered with
a sheet of asbestos, and two round burners were added. This boiler would hold
a steam pressure of about 15 pounds and run the engine slowly; but if the pres-
sure were allowed to rise to 60 pounds, the engine would drive a 2-foot propel-
ler of 18-inch piteh at the rate of about 650 turns per minute for from 80 to 90
seconds, while the steam ran down to 10 pounds, showing that this boiler, at
least, was too small. This was further shown in a trial of the plain coil made
in October, 1891; 6 pounds of water were evaporated in 32 minutes under a pres-
sure of 60 pounds. This was at the rate of 11.25 pounds per hour, or, taking
the U. 8. Centennial standard of 30 pounds of evaporation per horse-power,
gave an available output of less than 4 horse-power.

With these results before me, I decided to make a trial of the ‘‘ beehive ”’
principle upon a smaller seale than in the boiler designed for Aerodrome No. 0.
I used a small boiler of which the inner coil consisted of 8 turns of 3-inch eop-
per tube about 28 gauge thick, and the outer coil of 11 turns of 4-inch copper pipe.
This gave 12 feet of 2-inch, and 16 feet of 14-inch tubing. The drum was of No.
27 gauge, hard planished copper. With this boiler consuming 6 oz. of fuel, 80.3
oz. of water were evaporated in 28 minutes, or at the rate of about 10.75 pounds
per hour. As these coils contained but 2.22 square feet of heating surface, and
as the three to be built would contain 3.7 square feet each, it was estimated the

36 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE ., vou. 27

10 square feet afforded by them could safely be depended upon to provide steam
for a 1 horse-power engine. As far as fuel consumption was concerned, the rate
of evaporation was about 15.6 pounds of water per pound of gasoline, all of
which was satisfactory.

The burner originally designed for use in connection with the ‘‘ beehive ”’
boilers, consisted of a small tank in which a quantity of gasoline was placed, the
space above being filled with compressed air. Rising from the bottom of this
tank was a small pipe coiling back and down and ending in an upturned jet from
which the gas generated in the coil would issue. The burner thus served to
generate its own gas and act as a heater for the boilers at the same time.

In the construction of Aerodrome No. 0, four of the ‘‘ beehive ’’ coils were
placed in a line fore and aft. The fuel tank was located immediately back of the
rear coil and consisted of a copper cylinder 11 em. in diameter and 9 em. long.
The engines were placed immediately in front of the coils, all the apparatus
being enclosed in a light framing, as shown in the photograph (Plate 10).

Extending front and back from the hull were the tubes for supporting the
wings and tail, each one metre in length. The cross-framing for carrying the
propeller shafts was built of tubing 1.5 em. diameter, and the shafts themselves
were of the same size. The ribs of the hull were rings made of angle-irons
measuring 1.50 1.75 em., which were held in place longitudinally by five 0.7 em.
channel bars.

As it had been learned in the preliminary experiments with the model ‘‘ bee-
hive ’’ boiler that the heated water would not of itself cause a sufficiently rapid
circulation to be maintained through the tubes to prevent them from becoming
red-hot, two circulating pumps were added for forcing the water through the
coils of the two forward and two rear boilers respectively, the water being taken
from the lower side of the drum and delivered into the bottom of the coils, which
were united at that point for the purpose. A worm was placed upon each of the
propeller shafts, just back of the engines, meshing in with a gear on a crank-
shaft from which the pumps were driven. This shaft rotated at the rate of 1 to
24, so that for 1200 revolutions of the engine, it would make but 50, driving a
single-acting plunger 1.2 em. in diameter and 2 em. stroke.

Apparently all was going well until I began to try the apparatus. First,
there was a difficulty with the burner, which could not be made to give forth the
relative amount of heat that had been obtained from the smaller model, and
steam could not be maintained. With one ‘‘ beehive ’’ connected with the com-
pound engine, and a 70 em. propeller on the shaft, there were about 250 turns
per minute for a space of about 50 seconds, in which time the steam would fall
from 90 pounds to 25 pounds, and the engine would stop. Then, as we had no
air-chamber on the pumps at the time, they would not drive the water through
the coils. Subsequent experiments, however, showed that the boilers could be

ee

i=

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 37
depended upon to supply the steam that the compound engines would require ;
but after the whole was completed, the weight, if nothing else, was prohibitory.

I had gone on from one thing to another, adding a little here and a little
there, strengthening this part and that, until when the hull was finally completed
with the engines and boilers in place, ready for the application of the wings, the
weight of the whole was found (allowing 7 pounds for the weight of the wings
and tail) to be almost exactly 45 pounds, and nearly 52 pounds with fuel and
water. To this excessive weight would have to be added that of the propellers,
and as the wings would necessarily have to be made very large in order to carry
the machine, and as the difficulties of launching had still to be met, nothing was
attempted in the way of field trials, and with great disappointment the decision
was made in May, 1892 (wisely, as it subsequently appeared) to proceed no
further with this special apparatus.

However, inasmuch as this aerodrome with its engines and boilers had been
completed at considerable expense, it was decided to use the apparatus as far
as it might be practicable, in order to learn what must be done to secure a
greater amount of success in the future. The fundamental trouble was to get
heat. In the first place there was trouble with the burners, for it seemed to be
impossible to get one that would vaporize the gasoline in sufficient quantity to
do the work, and various forms were successively tried.

All of the early part of 1892 was passed in trying to get the boilers to work
at a steam pressure of 100 pounds per square inch. On account of the defects
in the tubes and elsewhere this required much patient labor. The writer, even
thus early, devised a plan of using a sort of aeolipile, which should actuate its
own blast, but this had to be abandoned on account of the fact that the pear-
shaped receivers would not stand the heat. This necessitated a number of ex-
periments in the distillation of gas, in the course of which there was trouble
with the pumps, and a continual series of breakages and leakages, so that the
middle of April came before I had secured any further satisfaction than to dem-
onstrate that possibly the boilers might have a capacity sufficient for the work
laid out for them to do; but subsequent experiments showed that even in this
I was mistaken, for it was only after additional jets had been put in between the
coils that I succeeded in getting an effective horse-power of 0.43 out of the
combination.

Finally, on the 14th of April, after having reduced the capacity of the pumps
to the dimensions given above (for the stroke was originally 1.25 inch) I obtained
the development of 1 full horse-power by the engine for 41 seconds, with a steam
pressure of 100 pounds per square inch, and a rate of revolution of 720 per
minute. But at the end of this brief period, the shafts sprung and the worm
was thrown out of gear.

38 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

I pass over numerous other experiments, for their only result was to make
it clear that the aerodrome, as it had been constructed, could not be made to
work efficiently, even if its great weight had not served as a bar to its flight. It
was, therefore, decided to proceed with the construction of another.

After the failure of the first steam-driven model No. 0, which has just been
described, subsequent light models were constructed. These, three in number,
made with a view to the employment of carbonic acid or compressed air, but
also to the possible use of steam, are shown in Plate 10, Nos. 1, 2, 3; on the same
scale as the larger model which had preceded them. In describing these, it will
be well to mention constructive features which were experimented on in them,
as well as to describe the engines used.

In No. 1, which was intended to be on about 2 the linear scale of No. 0, the
constructive fault of the latter, that of making the support depend on a too
flexible hull, was avoided, and the straight steel tube (‘‘ midrod ”’ it will hereafter
be called) was carried through from end to end, though at the cost of incon-
venience in the placing of the machinery, in what may be called the hull, which
now became simply a protective case built around this midrod. The mistaken
device of the long shafts meeting at an angle was, however, retained, and the
engines first tried were a pair of very light ones of crude construction.

These were later replaced by a pair of oscillating engines, each 3 em. di-
ameter by 3 em. stroke, with a combined capacity of 42 cubie em. and without
cut-off. The midrod was made of light steel tubing 2 em. outside diameter.
The framing for the hull was formed by a single ring of U section, 8 em. across
and 18 em. in depth, stayed by five ribs of wood measuring 0.70.3 em. The in-
clined propeller shafts, which were connected by a pair of bevel gears as in No.
0, were made of tubing 0.5 em. outside diameter, and were intended to turn pro-
pellers of from 40 to 45 em. in diameter. The weight, without engine or reservoir
for gas, was 1161 grammes. With a weight equivalent to that of the intended
reservoir and engines plus that of the proposed supporting surfaces, the whole
weight, independent of fuel or water, was 2.2 kilogrammes.

The engines, which were not strong enough to sustain a pressure of over 2
atmospheres, at an actual pressure of 20 pounds drove the 45 em. propellers
through the long V shafts and lifted only about + of the flying weight of the ma-
chine. The power developed at the Prony brake was collectively only about .04
horse-power, giving 1200 turns a minute to two 40 em. propellers. This was the
best result obtained.

This aerodrome was completed in June, 1892, but changes in the engines and
other attempted improvements kept it under experiment until November of that
year, when it appeared to be inexpedient to do anything more with it

Aerodrome No. 2 (see Plate 10), was a still smaller and still lighter construe-
tion, in which, however, the midrod was bent (not clearly shown in the photo-

SS a

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 39

graph), so as to afford more room in the hull. This introduced a constructional
weakness which was not compensated by the added convenience, but the princi-
pal improvement was the abandonment of the inclined propeller shafts, which
was done at the suggestion of Mr. J. KE. Watkins, so that the propellers were
carried on parallel shafts as in marine practice. These parallel shafts were
driven by two very small engines with cylinders 2.3 em. in diameter by 4 cm.
stroke, with a collective capacity of 33 cu. em. and without cut-off, which were
mounted on a cross-frame attached to the midrod at right angles near the rear
end of the hull.

These engines, driven either by steam or by earbonic-acid gas developed
0.035 horse-power at the Prony brake, giving 750 revolutions of the 45 em. pro-
pellers, and lifting about + of the total weight which it was necessary to provide
for in actual flight. A higher rate of revolution and a better lift were occasion-
ally obtained, but there was little more hope with this than with the preceding
models of obtaining power enough to support the actual weight in flight, although
such sacrifices had been made for lightness that every portion of the little model
had been reduced to what seemed the limit of possible frailty consistent with
anything like safety. Thus the midrod was lighter than that of No. 1, bemg
only 1 em. in outside diameter. The frame was made of thin wooden strips 5
mm.X3.5 mm., united by light steel rings. The cross framing carrying the en-
gines was also of wood, and was formed of four strips, each 7 mm. X 3 mm.
The shafts were but 4 mm. in diameter.

As these engines did not give results that were satisfactory, when using
carbonic-acid gas, experiments were commenced to secure a boiler that would
furnish the requisite steam. As the ‘‘ beehive ’’ boiler had proved to be too
heavy, and as the steam obtained from it had been inadequate to the require-
ments, something else had to be devised. A few of the boilers used in 1892 are
shown in Fig. 3. The one marked 4 is one of the ‘‘ beehives,’’ while an ele-
ment of another form tried is that marked B. It consisted of 2-inch copper tubes
joined to a drum of 10-0z. copper. This was made in May, 1892, and was tested
to a pressure of 50 atmospheres, when it burst without any tearing of the metal.

In July another boiler like that shown at C in Fig. 38 was made. This
was formed of tubes 3 em. in diameter, and weighed 348 grammes. It carried
about 300 grammes of water and stood a steam pressure of 125 pounds per
square inch, but failed to maintain sufficient steam pressure.

Accordingly, in the same month, a third boiler like that shown at D was built.
It consisted of a tube 12 inches long to which were attached fifteen 41-inch tubes
each 7 inches long, in the manner shown. The heating surface of this boiler,
including the tubes and the lower half of the drum, amounted to 750 square em.,
and it was thought that this would be sufficient to supply steam for a flight of a

40 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

minute and a half. But when a test was made, it also was found to be deficient
in steaming power even after changes were made in it which occupied much time.

By the first of October, 1892, there had been built one large aerodrome that
could not possibly fly, a smaller one, No. 1, on 2 the linear scale of No. 0, with
a pair of engines but no means of driving them, and the still smaller No. 2 with
a boiler that was yet untried.

Aerodrome No. 3 (Plate 10) was an attempt to obtain better conditions than
had existed in the preceding model without any radical change except that of
moving the cross frame, which carried the engines and propellers, nearer the
front of the machine. Instead of the oscillatory engines used up to this time,
two stationary cylinder engines, each 2.4 cm. in diameter and 4 em. stroke, havy-
ing a combined capacity of 36 cu. em. without cut-off were employed for driving
the propellers. The engines, though occasionally run in trials with steam from
a stationary boiler, were intended to be actuated either by compressed air or
carbonic-acid gas contained in a reservoir which was not actually constructed,
but whose weight was provisionally estimated at 1 kilogramme. The weight of
the aerodrome without this reservoir was but 1050 grammes, including the esti-
mated weight of the sustaining surfaces, which consisted principally of two wings,
each about 1 metre in length by 30 em. in breadth and which were in fact so slight
in their construction, that it is now certain that they could not have retained their
shape in actual flight.

The only trials made with this aerodrome, then, were in the shop, of which
it is sufficient to cite those of November 22, 1892, when under a pressure of 30
pounds, the maximum which the engines would bear, two 50 em. propellers were
driven at 900 revolutions per minute, with an estimated horse-power of 0.07,
about 35 per cent of the weight of the whole machine being lifted. This was a
much more encouraging result than any which had preceded, and indicated that
it was possible to make an actual flight with the aerodrome if the boilers could
be ignored, the best result having been obtained only with carbonic acid supplied
without limit from a neighboring ample reservoir.

This aerodrome was also tested while mounted upon a whirling-arm and
allowed to operate during its advance through the air. The conclusion reached
with it at the close of 1892, after a large part of the year passed in experiments
with carbonic-acid gas and compressed air, was that it was necessary to revert
to steam, and that whatever difficulties lay in the way, some means must be found
of getting sufficient power without the weight which had proved prohibitory in
No. 0.

With this chapter, then, and with the end of the year 1892, I close this very
brief account of between one and two years of fruitless experiment in the con-
struction of models supplied with various motors, subsequent to and on a larger
scale indeed than the toy-like ones of india rubber, but not even so efficient as

those had been, since they had never procured a single actual flight.

——————

—

ee eee

a ee

at

_ ere

CHAPTER V
ON SUSTAINING SURFACES

The following general considerations may conveniently precede the particu-
lar description of the balancing of the aerodrome.

In ‘‘ Experiments in Aerodynamics,’’ I have given the result of trials, show-
ing that the pressure (or total resistance) of a wind on a surface 1 foot square,
moving normally at the velocity of 1 foot per second, is 0.00166 pounds, and that
this pressure increases directly as the surface of the plane, and (within our ex-
perimental condition) as the square of the velocity,’ results in general accord-
ance with those of earlier observers.

I have further shown by independent investigations that while the shape of
the plane is of secondary importance if its movement be normal, the shape and
“aspect ”’ greatly affect the resultant pressure when the plane is inclined at a
small angle, and propelled by such a force that its flight is horizontal, that is,
under the actual conditions of soaring flight.

I have given on page 60 of ‘‘ Aerodynamics,’’ the primary equations,

P=P,.F(@)=kAV’F (a), -

W=P, cos a=kAV°F (a) cos a,

R=P, sin a=kAV*F (a) sina,
where W is the weight of the plane under examination (sometimes called the
“lift”’); R the horizontal component of pressure (sometimes called the ‘‘drift’’) ;
k is the constant already given; A the area in square feet; V. the velocity in feet
per second; F’ a function of « (to be determined by experiment); « the angle
which, under these conditions, gives horizontal flight.

I have also given on page 66 of the same work the following table showing
the actual values obtained by experiment on a plane, 304.8 inches (=1 sq. ft.),
weighing 500 grammes (1.1 pounds) :

Weight with planes
Soaring speed Horizontal Work expended of like form that
Angle Wee pressure per minute 1 horse-power will
with : R. 60 RV. drive through the air
horizon at velocity V.
a. —— <— — - — —)
Metres Feet A Kilogram Foot- Kilo-
per second. | per second. | “T#™mes. metres. | pounds.| grammes. EEE s
45° 11.2 36.7 500 536 2,454 6.8 15
30 10.6 34.8 275 175 1,268 13.0 29
15 11.2 36.7 128 86 623 26.5 58
10 12.4 40.7 88 65 474 34.8 De
5 15.2 49.8 45 41 | 297 55.5 122
2 20.0 65.6 20 24 | 174 95.0 209
|

*This pressure per unit of area varies with the area itself, but in a degree which is negligible
for our immediate purpose.
4]

42 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vob. 27

It cannot be too clearly kept in mind that these values refer to horizontal
flight, and that for this the weight, the work, the area, the angle and the velocity
are inseparably connected by the formule already given.

It is to be constantly remembered also, that they apply to results obtained
under almost perfect theoretical conditions as regards not only the maintenance
of equilibrium and horizontality, but also the rigid maintenance of the angle «
and the comparative absence of friction, and that these conditions are especi-
ally ‘‘ theoretical ’’ in their exclusion of the internal work of the wind observ-

able in experiments made in the open wind.

EXPERIMENTS IN THE Open WIND

T have pointed out * that an mdefinite source of power for the maintenance
of mechanical flight, lies in what I have called the ‘‘ internal work ’’ of the
wind. It is easy to see that the actual effect of the free wind, which is filled with
almost infinitely numerous and incessant changes of velocity and direction, must
differ widely from that of a uniform wind such as mathematicians and physi-
cists have almost invariably contemplated in their discussions.

Now the artificial wind produced by the whirling-table differs from the real
wind not only in being caused by the advancing object, whose direction is not
strictly linear, and in other comparatively negligible particulars, but especially
in this, that in spite of little artificial currents the movement on the whole is
regular and uniform to a degree strikingly in contrast with that of the open wind
in nature.

In a note to the French edition of my work, I have ealled the attention of the
reader to the fact that the figures given in the Smithsonian publication can
show only a small part of the virtual work of the wind, while the plane, which is
used for simplicity of exposition, is not the most advantageous form for flight;
so that, as I go on to state, the realization of the actually successful aerodrome
must take account of the more complex conditions actually existing in nature,
which were only alluded to in the memoir, whose object was to bring to attention
the little considered importance of the then almost unobserved and unstudied
minute fluctuations which constitute the internal work of the wind. I added
that I might later publish some experimental investigations on the superior effi-
ciency of the real wind over that artificially created. The experiments which
were thus alluded to in 1893, were sufficient to indicate the importance of the sub-
ject, but the data have not been preserved.

What immediately follows refers, it will be observed, more particularly to

the work of the whirling-table.

2See “Internal Work of the Wind”; also Revue de L’Aeronautique, 5° Livraison, 1893.

SIS AWE Sa tart tem A ly By Wa i A et PS kl em a ie

be as

eave

es aa |

bol 8

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 43

Renation or ArEA TO WEIGHT AND PoweErR

In order to get a more precise idea of the character of the alteration intro-
duced into these theoretical conditions by the variation of any of them, let us,
still confining ourselves to the use of the wluirling-table, suppose that the plane
in question while possessing the same weight, shape, and angle of inclination,
were to have its area increased, and to fix our ideas, we will suppose that it be-
came 4 square feet instead of 1 as before. Then, from what has already been
said, V’, the velocity, must vary inversely as the square root of the area; that is,
it must, under the given condition, become one-half of what it had been, for if
V did not alter, the impelling force continuing the same, the plane would rise
and its flight no longer be horizontal, unless the weight, now supposed to be con-
stant, were itself increased so as to restore horizontality.

I have repeated Table XIII under the condition that the area be quadrupled,
while all the other conditions remain constant, except the soarimg speed, which
must vary.

Work. | Weight.
Soaring speed TT aeiwer ila
a (feet per second) | Work expended per Weight of like planes
Vi. minute. which 1 H.P. will drive
A = 4 3q. ft. through the air with
| W= 500 gr. = 1.1 Ibs. velocity V’.
|
|
| Foot-pouvnds. | Pounds.
45° 18.4 1,217 | 30
30 | 17.4 | 634 57
Lor|| 18.4 | 312 H 116
10 | 20 4 | 237 | 154
5 2479 148 244
2 | 32.8 87 418

W is the weight of the single plane; A is the area; F is the horizontal “ drift.” Wt is the weight
of like planes which 1 H. P. will drive at velocity V. Work is RV.

I. If Work is constant, R varies as *VA. II. If R is constant, Work varies as a Ill. If W

is constant while A varies, the weight which 1 H. P. will support varies as VA.

The reader is reminded that these are simply deductions from the equations
given in ‘‘ Aerodynamies,’’ and that these deductions have not been verified by
direct trial, such as would show that no new conditions have in fact been intro-
duced in this new application. While, however, these deductions cannot convey
any confidence beyond what is warranted by the original experiments, in their
general trustworthiness as working formule at this stage of the investigations,
we may, I think, feel confidence.

I may, in view of its importance, repeat my remark that the relation of area
and weight which obtain in practice, will depend upon yet other than these theo-
retical considerations, for, as the flight of the free aerodrome cannot be ex-
pected to be exactly horizontal nor maintained at any constant small angle, the

44 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 2
data of ‘‘ Aerodynamics ’’ (obtained in constrained horizontal flight with the
whirling-table) are here insufficient. They are insufficient also because these
values are obtained with small rigid planes, while the surfaces we are now to use
cannot be made rigid under the necessary requirements of weight, without the
use of guy wires ‘and other adjuncts which introduce head resistance.

Against all these unfavorable conditions we have the favoring one that, other
thines being equal, somewhat more efficiency can be obtained with suitable curved
surfaces than with planes.* :

I have made numerous experiments with curves of various forms upon the
whirling-table, and constructed many such supporting surfaces, some of which
have been tested in actual flight. It might be expected that fuller results from
these experiments should be given than those now presented here, but Tam
not yet prepared to offer any more detailed evidence at present for the perform-
ance of curved surfaces than will be found in Part III.‘ I do not question that
curves are in some degree more efficient, but the extreme increase of efficiency in
curves over planes understood to be asserted by Lilienthal and by Wellner, ap-
pears to have been associated either with some imperfect enunciation of condi-
tions which gave little more than an apparent advantage, or with conditions
nearly impossible for us to obtain in actual flight.

All these circumstances considered, we may anticipate that the power re-
quired (or the proportion of supporting area to weight) will be very much greater
in actual than in theoretical (that is, in constrained horizontal) flight, and the
early experiments with rubber-driven models were in fact successful only when
there were from three to four feet of sustaining surface to a pound of weight.
When such a relatively large area is sought in a large aerodrome, the construc-
tion of light, yet rigid, supporting surfaces becomes a nearly insuperable diffi-
culty, and this must be remembered as consequently affecting the question of the
construction of boiler, engines and hulls, whose weight cannot be increased with-
out increasing the wing area.

*More recent experiments conducted under my direction by Mr. Huffaker give similar results,
but confirm my earlier and cruder observations that the curve, used alone, for small angles, is much
more unstable than the plane.

*As stated in the Preface, Part III has not yet been prepared for publication.

CHAPTER VI
BALANCING THE AERODROME

By ‘‘ balancing ’’ I mean such an adjustment of the mean center of pressure
of the supporting surfaces with reference to the center of gravity and to the line
of thrust, that for a given speed the aerodrome will be in equilibrium, and will
maintain steady horizontal flight. ‘‘ Balance ’’ and ‘‘ equilibrium ’’ as here used
are nearly convertible terms.

Lateral STABILITY

Equilibrium may be considered with reference to lateral or longitudinal sta-
bility. The lateral part is approximately secured with comparative ease, by im-
itating Nature’s plan, and setting the wings at a diedral angle, which I have usu-
ally made 150°. Stability in this sense cannot be secured in what at first seems
an obvious way—by putting a considerable weight in the central plane and far
below the center of gravity of the aerodrome proper, for this introduces rolling.
Thence ensues the necessity of carrying the center of gravity more nearly up
to the center of pressure than would otherwise be necessary, and so far introdue-
ing conditions which tend to instability, but which seem to be imposed upon us
by the circumstances of actual flight. With these brief considerations concern-
ing lateral stability, I pass on to the far more difficult subject of longitudinal
stability.

LONGITUDINAL STABILITY

My most primitive observation with small gliding models was of the fact
that greater stability was obtained with two pairs of wings, one behind the
other, than with one pair (greater, that is, in the absence of any instinctive
power of adjustment).

This is connected with the fact that the upward pressure of the air upon
both pairs may be resolved into a single point which I will call the ‘‘ center of
pressure,’’ and which, in stable flight, should (apart from the disturbance by the
propeller thrust) be over the center of gravity. The center of pressure in an
advancing inclined plane in soaring flight is, as I have shown in ‘‘ Aerodynam-
ics,’’ and as is otherwise well known, always in advance of the center of figure,
and moves forward as the angle of inclination of the sustaining surfaces dimin-
ishes, and, to a less extent, as horizontal flight increases in velocity. These facts
furnish the elementary ideas necessary in discussing this problem of equilibrium,
whose solution is of the most vital importance to successful flight.

46 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE Vou. 27

The solution would be comparatively simple if the position of the CP could
be accurately known beforehand, but how difficult the solution is may be realized
from a consideration of one of the facts just stated, namely, that the position
of the center of pressure in horizontal flight shifts with the velocity of the flight
itself, much as though in marine navigation the trim of a steamboat’s hull were
to be completely altered at every change of speed. It may be remarked here
that the center of pressure, from the symmetry of the aerodrome, necessarily
lies in the vertical medial plane, but it may be considered with reference to its
position either in the plane XY (cp,) or in the plane YZ (cp.). The latter cen-
ter of pressure, as referred to in the plane YZ, is here approximately calculated
on the assumption that it lies in the intersection of this vertical plane by a hori-
zontal one passing through the wings half way from root to tip.

Experiments made in Washington, later than those given in ‘‘ Aerodynam-
ics,’’ show that the center of pressure, (cp,) on a plane at slight angles of inclina-
tion, may be at least as far forward as one-sixth the width from the front edge.
From these later experiments it appears probable also that the center of pres-
sure moves forward for an increased speed even when there has been no percep-
tible diminution of the angle of the plane with the horizon, but these considera-
tions are of little value as applied to curved wings such as are here used. Some
observations of a very general nature may, however, be made with regard to the
position of the wings and tail.

In the case where there are two pairs of wings, one following the other, the
rear pair is less efficient in an indefinite degree than the front, but the action
of the wings is greatly modified by their position with reference to the propel-
lers, and from so many other causes, that, as a result of a great deal of experi-
ment, it seems almost impossible at this time to lay down any absolute rule with
regard to the center of pressure of any pair of curved wings used in practice.

Later experiments conducted under my direction by Mr. E. C. Huffaker,
some of which will appear in Part ITI, indicate that upon the curved surfaces [|
employed, the center of pressure moves forward with an increase in the (small)
angle of elevation, and backward with a decrease, so that it may le even behind
the center of the surface. Since for some surfaces the center of pressure moves
backward, and for others forward, it would seem that there might be some other
surface for which it will be fixed. Such a surface in fact appears to exist in the
wing of the soaring bird. These experiments have been chiefly with rigid sur-
faces, and though some have been made with elastic rear surfaces, these have
not been carried far enough to give positive results.

The curved wings used on the aerodromes in late years have a rise of one
in twelve, or in some eases of one in eighteen,’ and for these latter the following

empirical local rule has been adopted:

+See footnote page 47.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 47

The center of pressure on each wing with a horizontal motion of 2000 feet
per minute, is two-fifths of the distance from front to rear. Where there are
two pair of wings of equal size, one following the other, and placed at such a
distance apart and with such a relation to the propellers as here used, the fol-
lowing wing is assumed to have two-thirds of the efficiency of the leader per unit
of surface. If it is half the size of the leader, the efficiency is assumed to be one-
half per unit of surface. If it is half as large again as the leader, its efficiency
is assumed to be eight-tenths per unit of surface. For intermediate sizes of fol-
lowing wing, intermediate values of the efficiency may be assumed.

These rules are purely empirical and only approximate. As approxima-
tions, they are useful in giving a preliminary balance, but the exact position of
the center of pressure is rarely determinable in either the horizontal or vertical
plane, except by experiment in actual flight. The position of the center of grav-
ity is found with all needed precision by suspending the aerodrome by a plumb-
line in two positions, and noting the point of intersection of the traces of the
line, and this method is so superior to that by calculation, that it will probably
continue in use even for much larger constructions than the present.

The principal factor in the adjustment is the position of the wings with ref-
erence to the center of gravity, but the aerodrome is moved forward by the thrust
of its propellers, and we must next recall the fact of experiment that as it is for
constructional reasons difficult to bring the thrust line in the plane of the cen-
ter of pressure of the wings, it is in practice sufficiently below them to tend to tip
the front of the aerodrome upward, so that it may be that equilibrium will be
attained only when CP, is not over CG.

In the discussiow of the equilibrium, then, we must consider also the effect
of thrust, and usually assume that this thrust-line is at some appreciable distance
below the center of pressure.

We may conveniently consider two cases:

1. That the center of pressure is not directly over the center of gravity; that
is, CG,—CP,=a, and estimate what the value of a should be in order that, dur-
ing horizontal flight, the aerodrome itself shall be horizontal; or,

1 According to Wellner (“ Zeitschrift fiir Luftschiffahrt,”’ Beilage, 1893), in a curved surface
with 1/12 rise, if the angle of inclination of the chord of the surface be a, and the angle between
the direction of resultant air pressure and the normal to the direction of motion be 3, then B<@ and
the soaring speed is
= i2 1

— sg) 2 =
K ~ F(a) xX cos Bp
while the efficiency is
W Weight
R Resistance
The following values were derived from experiments in the wind:

= tan 8

a—=—3° 0° +3° 6° go 12°
(a) = 0220 0.86 0.75 0.90 1.00 1.05
Tan Bi= 0:01 0.02 0.03 0.04 0.10 0.17

so that according to him, a curved surface shows finite soaring speeds when the angle of inclination
is 0° or even slightly negative.

48 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

2. Consider that the center of pressure is directly over the center of gravity
(CP,—CG,=0), and in this case inquire what angle the aerodrome itself may
take during horizontal flight.

First case. The diagram (Fig. 4) represents the resultants of the separate
system of forces acting on the aerodrome, and these resultants will lie in a verti-
cal medial plane from the symmetry of their disposition.

Let af represent the resultant of the vertical components of the pressure on
the wings; the horizontal component will lie in the line ae.

Fic. 4. Diagram showing relation under certain conditions of thrust, C. P. and C. G.

Let the center of gravity be in the line bd, and the resultant thrust of the
propellers be represented by cd.

Let W=weight of aerodrome.

Let 7=thrust of propellers.

Then if we neglect the horizontal hull resistance, which is small in comparison
with the weight, equilibrium obtains when W xab=T xbd.

Second case. The diagram (Fig. 5) represents the same system of forces
as Fig. 4, but in this case the point of support is directly over the center of
gravity g, when the axis of the aerodrome is horizontal.

Let W=weight of aerodrome.

Let T=thrust of the propellers.

Let R=distance of CG, below CP.=ag.

Let S=distance of thrust-line below CP.=ad.

If now the aerodrome under the action of the propellers be supposed to
turn about the CP, (or, a) through an angle a, so that g takes the position g’, we

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 49

obtain by the decomposition of the force of gravity an element g’/k=W sin «
which acts in a direction parallel to the thrust-line.

If we again neglect the horizontal hull resistance, equilibrium will be ob-
tained when

kg’ Xag’=T xad’

or WR sin a=TS
LS,
WR°

..&4=sin —

Fig. 5. Diagram showing relation under certain conditions of thrust, C. P. and C. G.

The practical application of these rules is greatly limited by the uncertainty
that attaches to the actual position of the center of pressure, and this fact and
also the numerical values involved may be illustrated by examples.

Conpition or ArroproMe No. 6, NovemsBer 28, 1896

The weight was 12.5 kilos. On November 28, the steam pressure was less
than 100 pounds, and the thrust may be taken at 4.5 kilos. The distance bd was
25 em.

Hence 12.5 x ab=4.5 x 25 cm.

ab=9 cm.

This appears to give the position of CP,, but CP; is a resultant of the pressure on
both wings, and its position is determined by the empirical rule just cited. We
5

50 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE Wore, 2

cannot tell in fact, then, with exactness how to adjust the wings so that CG,—CP,
may be 9 em., and equilibrium was in fact obtained in flight when (the empiri-
eally determined) CG,—CP,=3 em.

Again, let it be supposed that CP, was really over CG, ....The distance of the
center of gravity below the center of pressure is 43 em.=R.

4.5x25 _190

Then C=sine 2° nearly.
12.5x43 j

The doubt as to the actual position of the resultant center of pressure, then, ren-
ders the application of the rule uncertain. In practice, we are compelled (un-
fortunately) after first calculating the balance, by such rules as the above, and
after it has been thus found with approximate correctness, to try a preliminary
flight. Having witnessed the actual conditions of flight, we must then readjust
the position of the wings with reference to the center of gravity, arbitrarily,
within the range which is necessary. This readjustment should be small.

Fic. 6. Diagram showing effect of Penaud tail.

In the preceding discussion it has been assumed that, if there is a flat tail or
horizontal rudder, it supports no portion of the weight. This is not an indis-
pensable condition but it is very convenient, and we shall assume it.) Inithis
case the action of the so-called Pénaud rudder becomes easily intelligible. This
is a device, already referred to in Chapter IT, made by Alphonse Pénaud for the
automatic regulation of horizontal flight, and it is as beautiful as it is simple.

Let AB (Fig. 6) be a schematic representation of an aerodrome whose sup-
porting surface is Bb, and let it be inclined to the horizon at such an angle a
that its course at a given speed may be horizontal. So far it does not appear
that, if the aerodrome be disturbed from this horizontal course, there is any
self-regulating power which could restore it to its origimal course ; but now let
there be added a flat tail AC set at an angle —a with the wing. This tail serves
simply for direction, and not for the support of the aerodrome, which, as already
stated. is balanced so that the CG comes under the CP of the wing Bb.

It will be seen on a simple inspection that the tail under the given conditions
is horizontal, and that, presenting its edge to the wind of advance, it offers no
resistance to it, so that if the front rises and the angle a increases, the wind will
strike on the under side of the tail and thereby tend to raise the rear and depress

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT dL

the front again. If the angle « diminish, so that the front drops, the wind will
strike the upper surface of the tail, and equally restore the angle « to the amount
which is requisite to give horizontal flight. If the angle a is not chosen originally
with reference to the speed so as to give horizontal flight, the device will still
tend to continue the flight in the straight line which the conditions impose,
whether that be horizontal or not.

From this description of its action, it will be seen that the Pénaud tail has
the disadvantage of giving an undulatory flight, if the tail is made rigid. This
objection, however, can be easily overcome by giving to it a certain amount of
elasticity. It does not appear that Pénaud gave much attention to this feature,
but stress is laid upon it in the article ‘‘Flight,’’ in the ninth edition of the En-
cyclopedia Britannica, and I have introduced a simple device for securing it.

The complete success of the device implies a strictly uniform velocity and
other conditions which cannot well be fulfilled in practice. Nevertheless, it is as
efficient a contrivance for its object as has yet been obtained.

More elaborate devices have been proposed, and a number of them, depend-
ing for their efficiency upon the action of a variety of forces, have been con-
structed by the writer, one of which will be described later. This has the ad-
vantage that it tends to secure absolutely horizontal flight, but it is much inferior
in simplicity to the Pénaud tail.

Apart from considerations about the thrust, the CP is in practice always
almost directly over the CG, and this relationship is, according to what has been
suggested, obtained by moving the supporting surfaces relatively to the CG, or
vice versa, remembering, however, that, as these surfaces have weight, any move-
ment of them alters the CG of the whole, so that successive readjustments may
be needed. The adjustment is further complicated by another important con-
sideration, namely, that those parts which change their weight during flight (like
the water and the fuel) must be kept very near the CG. As the water and fuel
tanks are fixed, it appears, then, that the center of gravity of the whole is prac-
tically fixed also, and this consideration makes the adjustment a much more

difficult problem than it would be otherwise.?

*The following formule proposed by Mr. Chas. M. Manly show how the center of pressure may
be moved any desired distance either forward or backward without in any way affecting the center of
gravity, and by merely moving the front and rear wings the same amounts but in opposite direc-
tions, the total movement of each wing being in either case five times the amount that it is desired
to move the mean CP,, and the direction of movement of the front wing determining the direction
of movement of CP,.

In Figure 7, CPs, and CP, are the centers of pressure of the front and rear wings respectively;
the weights of the wings, which are assumed to be equal and concentrated at their centers of figure,
are represented by w, w, and a is the distance of the center of pressure in either wing from its center
of figure. The original mean center of pressure of the aerodrome is CP,, W is the weight of the
aerodrome, supposed to be concentrated at @G,, while m is the distance from CP; to CG.

Now, if we have assumed that the rear wing, being of the same size as the front one, has a lifting
effect of only 0.66, and on this assumption have calculated the proper relative positions of the front
and rear wings to cause the CP, to come directly over the CG,, and upon testing the aerodrome find

2 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

“

that it is too heavy in front and, therefore, wish to move the center of pressure forward an amount,
say b, without affecting the center of gravity, we can calculate the proper relative positions of the
front and rear wings in the following manner. While the aerodrome as a whole is balanced at the
point CG,, the weight of the wings is not balanced around this point, for the rear wing, owing to
its decreased lifting effect, is proportionately farther from CP, than the front wing. In order, there-
fore, to avoid moving the center of gravity of the machine as a whole, any movement of the wings
must be made in such a way as to cause the difference between the weight of the rear wing multi-
plied by its distance from CG, and the weight of the front wing multiplied by its distance from CG,
to equal a constant: that is,

w(m + a) — w(0.66m — a) = constant,
and

0.330m + 2wa= constant.

If now the wings be moyed so that CP, is moved forward a distance b, we may indicate the distance
from CG, to the new OP;» by 2, and equating the difference between the weight of the rear wing

GR

Sq
Fig. 8. Fia. 9.

Figs. 7-9. Diagrams illustrating formule for moving C. P. without disturbing C. G.

multiplied by its new distance from CG, and the weight of the front wing multiplied by its new
distance from (G,, and making this difference equal to the constant difference, we can calculate 2

in terms of m and J, as follows:

Fig. 8,
w(a+ 2) —w(0.66(2 + b) + b—a) =0.33wm + 2wa,

~.2=m- 5d.
Knowing 2, we readily find that the new distance from CP; to CG, equals:
0.66(2 + b) + b=0.66m + 5b.

In a similar manner we may calculate the proper relative positions of the front and rear wings
when we wish to move the center of pressure backward a distance, b, from the original CP, without

changing the position of CG, From Fig. 7, we have as before:

w(m + a) —w(0.66m — a) = constant,
0.33wm + 2wa— constant.

Fig. 9,
w (2, + a) —w(0.66(%,— b) —b— a) = 0.33wm + 2wa.

~.%,—m— dd.
Similarly we have for the new distance from CPyw to CG:
0.66(z, — b) — b= 0.66m — 5b.

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CHAPTER VIL

HISTORY OF CONSTRUCTION OF FRAME AND ENGINES OF
AERODROMES

During the years 1892 and 1893, it will be recalled, four aerodromes, known
as Nos. 0, 1, 2, and 3, had been built, which were of two general types of construc-
tion. First. that represented by No. 0, in which a radically weak hull was made
to support rods at the front and rear, to which the wings and tail were attached.
This aerodrome was abandoned on account of the inability to provide it with
sufficient power, as well as because of its constructional weakness. Second, that
type represented by Nos. 1, 2, and 3, in which a midrod was earried through
from front to rear, around which the hull supporting the machinery was built.
These models were much lighter than No. 0, but were all abandoned because
it was found impossible to propel even the lightest of them. While all these
machines were in the strictest sense failures, inasmuch as none of them was
ever equipped with supporting surfaces, yet the experience gained in the con-
struction of them was of the very greatest value in determining the points at
which strength was needed, and in indicating the mode of construction by which
strength and rigidity could be obtained.t

1893

Another aerodrome, known as No. 4 (shown in Plate 11), was designed in
the latter part of 1892, and by the end of March, 1893, its construction was well
under way. It was of the second type, in that the midrod was continuous, but
it differed from the preceding forms in having the machinery (boilers, burners,
and tanks) attached directly to the midrod, the hull now taking the form of a
mere protective sheathing. As in Nos. 2 and 3, two engines were used, which
were mounted on a cross-frame of light tubing attached to the midrod at right
angles. It had, as at first constructed, no provision for the generation of steam,
but only for carrying a reservoir of carbonic acid to supply gas for the engines.

The whole, including wings, tail, and engines, but without the carbonic acid
reservoir, weighed 1898 grammes (4.18 lbs.). A cylindrical reservoir, weighing
521 grammes (1.14 Ibs.) and capable of holding 1506 cu. em. (92 eu. in.) was
constructed for this purpose, and tested for 30 minutes with a pressure of 100

*Jt is to be remembered that these aerodromes were under incessant modifications, No. 4 for
instance, presenting successive changes which made of it in reality a number of different machines,
one merging by constant alterations into the other, though it still went under the same name. After
1895 the type of the models remained relatively constant, but during the first five years of the work,
constructions equal to the original building of at least eight or ten independent aerodromes were
made.

RQ

vo

e Se we wee ee

54 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

atmospheres. If the weight of the cylinder, with its contents and adjuncts, be
taken as 800 grammes (1.76 lbs.), the total weight of the aerodrome was 2698
grammes (9.95 lbs.). The wings were plane surfaces of silk, stretched over a
very light frame, with no intermediate ribs to prevent the wing from being com-
pletely distorted by the upward pressure of the air. Even if they had been suffi-
ciently strong and stiff, the total surface of both wings and tail was but 2601 sq.
em. (2.8 sq. ft.) 6r approximately 0.5 sq. ft. of supporting surface to the pound,
much less than was found adequate, even under the most favorable cireum-
stances. The weight was much more than had been contemplated when the
wings were designed, yet, if all the other features of the aerodrome had been
satisfactory, and sufficient power had been secured, the work of providing suit-
able supporting surfaces would have been attempted. But as it was found that
the engines when supplied with carbonic-acid gas were unable to develop any-
thing like the power necessary to propel the aerodrome, and that the construe-
tion could be greatly improved in many other ways, this aerodrome was entirely
rebuilt. The work of the engines with carbonic acid had been so completely un-
satisfactory that the idea was entirely abandoned, and no further attempts to
develop an efficient motor other than steam were made.

It now became realized more completely than ever before that the primary
requisite was to secure sufficient power, and that this could be obtained only by
the use of steam. This involved a number of problems, all of which would have
to be solved before any hope of a successful machine could be entertained. In
the first place, engines of sufficient power and strength, but of the lightest pos-
sible construction, must be built. Second, a boiler must be constructed of the
least possible weight, which would develop quickly and maintain steadily steam
at a high enough pressure to drive the engines. This demanded some form of
heating apparatus, which could work under the adverse condition of enclosure
in a narrow hull, and steadily supply enough heat to develop the relatively large
quantity of steam required by the engines.

The first of these problems, that of procuring suitable engines, was at least
temporarily solved by the construction of two engines with brass cylinders,
which had a diameter of 2.4 em. (0.95 in.), and a piston stroke of 5 em. (1.97 in.).
The valve was a simple slide-valve of the piston type, arranged to cut off steam
at one-half stroke. No packing was used for the piston or the valve, which were
turned to an accurate fit to the cylinder and the steam-chest respectively. In
the engines built up to this time, the parts had frequently been soldered together,
and a great deal of trouble and delay had arisen from this cause. In these new
engines, however, as strong and careful a construction was made as was possi-
ble within the very narrow limits of weight, with the result that the engines,
though by.no means as efficient as those constructed later, were used in all the
experiments of 1893 and also during the first part of 1894.

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 5)

As soon as these engines were completed, in February, 1893, a test was
made of one of the cylinders, steam being supplied from the boiler of the shop-
engine. The experiments were made with the Prony brake, and showed that at
a speed of 1000 revolutions per minute, the power developed from a single cylin-
der was 0.208 H. P., with a mean effective pressure in the cylinder of only about
21 pounds per square inch of piston area, allowing a loss of 25 per cent for the
internal resistance of the engine. This pressure was so much less than should
have been obtained with the steam pressure used, that it now seems evident that
the steam passages and ports were too small to admit and exhaust the steam with
sufficient rapidity to do the work with the same efficiency that is obtained in
common practice. This, however, was not immediately recognized. The piston
speed at 1000 R. P. M. was 328 feet per minute, at which speed the steam at a
pressure of 80 pounds should have been able to follow up the piston and main-
tain almost, if not quite, full boiler pressure to the point of eut-off, but it did
not do so.

The problem of generating steam was much more difficult and required a long
and tedious series of experiments, which consumed the greater part of the year
before any considerable degree of success had been attained. In the course of
these experiments many unexpected difficulties were encountered, which neces-
sitated the construction of special forms of apparatus, which will be described
at the proper point. Numerous features of construction, which seemed to be of
value when first conceived, but which proved useless when rigorously tested, will
be noted here, whenever a knowledge of their valuelessness may seem to be of
advantage to the reader.

The boiler was necessarily developed simultaneously with the development
of the heating apparatus, and in the following pages, as far as possible, they will
be treated together; but often for the sake of clearness and to avoid repetition,
separate treatment will be necessary.

At the beginning of these experiments, there was much doubt as to whether
aleohol or gasoline would be found most suitable for the immediate purpose.
An aleohol burner had been used in connection with the earliest aerodrome, No.
0, but from the results obtained with it at that time, there seemed to be little
reason to hope for success with it. It is to be premised that the problem, which
at first seemed insoluble, was no less than to produce steam for something like
1 H. P. by a fire-grate, which should oceupy only a few ecubie inches (about the
size of a clenched hand) and weigh but a few ounces. It had to be attacked,
however, and as alcohol offered the great advantage of high calorific properties
with freedom from all danger of explosion, it was at first used.

Early in 1893, it occurred to me to modify the burner so as to make it essen-
tially an aeolipile, and in April of that year the first experimental aeolipile model
shown at A (Plate 12) was made. It was very small and intended for the dem-

ee oe

56 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

onstration of a principle rather than for actual service, but the construction of
this small aeolipile was an epoch in the history of the aerodrome. It furnished
immensely more heat than anything that had preceded it, and weighed so little
and worked so well that in May the aeolipile marked Bb was made. In this de-
sign two pipes were led from the upper portion of the cylinder, one to a large
Bunsen burner which heated the boiler, the other to a small burner placed under
the tank to vaporize the aleohol. This was followed by the one shown at C,
wherein the heating burner was smaller and the gas pipe, leading to the main
burner, larger.

Figures D, E, F, and G (Plate 12) were really continuations and improve-
ments of the same idea. In C there was simply a tube or flue through the tank;
in I’, however, this tube discharged into a smoke-stack fastened to the end of the
cylinder, while in G the flue turned upward within the tank itself and discharged
into the short stack on top. The object of these changes was to increase the draft
and heating power of the small flame, so that the gas would be more rapidly
generated and a greater quantity be thus made available for use under the boiler
in a unit of time. They were, however, though improvements in a construction
which was itself a great advance, still inadequate to give out a sufficient amount
of heat to meet the excessive demands of the required quantity of steam. The boil-
ers in connection with which these aeolipiles were used must now be considered.

The first boiler # (Plate 13) made during this year was a double-coil boiler

of the Serpollet type, formed of 19 feet of copper tubing having an internal di-
ameter of about 4 inch. Attached to the boiler was a small vertical drum, from
the top of which steam was led to the engine, a pipe from the bottom leading to
the pump. This boiler was tested in April with an alcohol heater, the pump in
this trial bemg worked by hand. This apparatus developed a steam pressure
varying from 25 to 75 pounds, which caused the engines to drive a 60 em. pro-
peller of 1.25 pitch-ratio 565 revolutions per minute. The greatest difficulty was
experienced in securing a sufficient and uniform circulation in the boiler coils.
The action in the present case was extremely irregular, as the pressure some-
times rose to 150 pounds, driving the engines at a dangerous speed and bending
the eecentrie rod, while at other times it would fall so low that the engines stop-
ped completely.

As the pump used in this trial had proved so unsatisfactory and unreli-
able, it was replaced by a reservoir of water having an air-chamber charged to
10 atmospheres, the flow from which could apparently be regulated with the
greatest nicety by a needle valve at the point of egress; but for some reason
its performance was unsatisfactory and remained so after weeks of experiment.

There was used in connection with this device the double-coil boiler shown
at F’ (Plate 13) which was made of tubes flattened so as to be nearly capillary.
The idea of this was to obtain a larger heating surface and a smaller volume of

ayeye _

2 a =

ent:

jars

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

1894

CASOLINE BURNERS

1836

ij

i893 ALCOHOL AEOLIPILES jg94

1893 SEPARATORS 1895
i895

BURNERS, AEOLIPILES, AND SEPARATORS

VOL, 27, NO. 3, PL. 12

MITHSONIAN CONTRIBUTIONS TO KNOWLEDGE SoiceanG Stee

i393 BOILERS 893 1893 i894

i

"val daabiiy

Pree BOERS

BOILERS OF AERODROMES

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 57

water, so that by proper regulation at the needle valve, just that quantity would
be delivered which could be converted into steam in its passage through the
coils, and be ready for use in the engines as it left the boiler at the farther ex-
tremity. The results obtained from this were an improvement over those from
the original coil, and a third set of coils (G, in Plate 13) was made. This boiler
consisted of three flattened tubes superposed one over another.

These two boilers were tried by placing them in a charcoal fire and turning
on an alcohol blast, while water from a reservoir under constant air pressure
was forced through them past a pin valve. The result was that the two-stranded
coil supplied steam at from 10 to 40 pounds pressure to run the engines at about
400 revolutions per minute. The pressure rose steadily for about 40 seconds
and then suddenly fell away, though the coils were red-hot, and neither the water
nor the aleohol was exhausted—apparently because of the irregularity of the
supply of water, due to the time taken by it after passing the valve to fill the
considerable space intervening between that point and the boiler.

An attempt was made to overcome this difficulty by putting a stop-cock di-
rectly in front of the boiler so that the water, while still under the control of the
needle valve, could be turned in at once; the alcohol blast was also arranged to
be turned on or off at pleasure, and provision was made, by taking out the end
of the flue inclosing the boiler, to provide for an increased air supply. With this
arrangement a flame eight or nine inches long was obtained, but a test showed
that not more than 25 grammes of water per minute passed through the tubes,
which was not enough.

Further tests with these boilers were so far satisfactory as to show that
with the flattened-tube Serpollet boiler, comprising from 60 to 80 feet of tubing,
from 80 to 100 pounds pressure of steam could be maintained, but not steadily.
As there were difficulties in flattening the tubes to make a boiler of this sort, a
compromise was effected in the construction of the one shown at H (Plate 13),
which was made of light copper tubes 5 mm. in diameter, laid up in three lengths
of 6 metres each. The ends of these coils were so attached to each other that the
water entering at one end of the smallest coil would pass through it and then
enter the middle coil, whence it passed through the third or outer coil. Two
sets of these coils were made and placed in the thin sheathings shown in the
photograph. Repeated experiments with these boilers demonstrated that the
pressure did not rise high enough in proportion to the heat applied, and that
even the pressures obtained were irregular and untrustworthy. The principal
difficulty still lay in maintaining an active and uniform circulation through the
coils, and for this purpose the water reservoir under constant air pressure had
proved itself inadequate. This pointed to a return to the use of the force pump,
the construction of which had hitherto presented so many special difficulties that
it had been temporarily abandoned.

58 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

A further difficulty experienced in the use of these boilers had been that of
obtaining dry steam for the engines, as during the early experiments the steam
had been delivered directly into the engines from the boiler coils. But in August
the writer devised a chamber, known as the ‘‘ separator,’’ where it had an op-
portunity to separate from the water and issue as dry steam, or at least approxi-
mately dry steam. This was an arrangement familiar in principle to steam en-
gineers under another form, but it was one of the many things which, in the igno-
rance of steam engineering the writer has already freely admitted, he had to
reinvent for himself.

At about the same time, a new pump was designed to drive the water from
the bottom of the separator, which served the double purpose of steam drum and
reservoir, into the coils. This pump had a diameter of 4.8 em., and was run at
180 strokes per minute.

The result of the first experiments with these improvements demonstrated
that, within certain limits, the amount of water evaporated is proportional to the
circulation, and in this boiler the circulation was still the thing that was at fault.
Finally, the results of the experiments with the two-stranded, triple-coil boiler
may be summed up in the statement that it was possible to maintain a pressure
of 80 pounds, and that with it the engines could be made to develop from 0.3 to
0.4 H. P. at best. It weighed 650 grammes (1.48 pounds) without the asbestos
jacket.

About this time the writer had the good fortune to secure the temporary
services of Dr. Car] Barus, an accomplished physicist, with whose aid a great
variety of boilers were experimented on.

The next form of boiler tested was that shown at N (Plate 13), made on a
system of coils in parallel, of which there were twenty complete turns. In the
first test it generated but 20 pounds of steam, because the flame refused to work
in the colder coils. The work of this boiler was very unsatisfactory, and it was
only with the greatest diffienlty that more than ten pounds pressure could be
maintained. There was trouble, too, with the circulation, in that when the flame
was in full play the pump seemed to meet an almost solid resistance, so that it
could not be made to do its work.

A new boiler was accordingly made, consisting of three coils of four strands
each. With this the pump worked easily, but whereas it was expected to get 120
pounds pressure, the best that could be obtained was 70 pounds. The outer
coil was then stripped off, and a trial made in which everything ran smoothly
and the pressure mounted momentarily to 90 pounds. After some adjustment,
a mean pressure of 80 pounds was obtained, giving 730 revolutions of the en-
gine per minute, with an indicated horse-power of 0.32.

It was shown in this work that, within certain limits, steam is generated
most rapidly when it is used most rapidly, so that two engines could be used

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 59

almost as well as one, the reason apparently being that the rapid circulation in-
creased the steam generating power of the boiler, and that the engines worked
best at about 80 pounds. It was also found that a larger tubing was better than
the small, weight for weight, this fact bemg due to the greater ease with which
circulation could be maintained, since fewer coils were necessary in order to
obtain the same external heating surface. The pressure in the coils and the
separator was also much more nearly equalized. The result was that the boiler
temporarily approved was one made of tubing 6.85 mm. (0.25 inch) in diameter,
bent into a two-coil, two-stranded boiler, having sixteen complete turns for each
strand in each coil. The total weight was 560 grammes (1.23 pounds) with a
total heating surface of 1300 sq. em. (1.4 sq. ft.).

The separator used in the experiments made during August and September
was of a form in which the water was forced below a series of partitions that
prevented it from following the steam over into the cylinders of the engines. It
weighed 410 grammes (0.9 pound) and was most conveniently worked with 700
grammes (1.54 pounds) of water. The boiler and separator together weighed
970 grammes (2.1 pounds).

A new separator was, however, designed, which was horizontal instead of
vertical, as it was intended that it should be placed just below the midrod. An-
other form, devised for constructional reasons, consisted of a cylinder in which
a pump was imbedded. Heretofore the pump used had been single-acting, but it
was now proposed to make a double-acting pump. Upon testing this apparatus,
it was found that when using an aeolipile, it took 150 grammes of alcohol to
evaporate 600 grammes of water. It was evident that the latter was used very
wastefully, so that the thermal efficiency of the engine was not over one per cent ;
but it was also evident that, under the necessity of sacrificmg everything to light-
ness, this waste was largely inevitable.

About the middle of October, another boiler (O, Plate 18) was made, which
consisted of two coils wound in right and left hand screw-threads, one fitting
loosely over the other, so as to make a cylindrical lattice-work 32 em. (12.6 in.)
long. Each coil contained two strands of copper tube 0.8 mm. thick, and weigh-
ing 54 grammes to the metre (0.036 pound to the foot). The inner coil had a
diameter of 5.63 em. (2.22 in.), with nine turns of tube to the strand, the two
strands making a length of 319 em. (10.5 feet) for the coil. The outer coil had
a mean diameter of 6.88 em. (2.71 in.) and a length of 388 em. (12.7 feet) for the
two strands. The total length of the two coils was, therefore, 707 cm. (23.2 feet),
with a heating surface of about 1415 sq. em. (1.52 sq. ft.) and a total weight of
382 grammes (0.84 pound).

The results obtained with this boiler were so far satisfactory as to show that,
under the most favorable conditions, when air was supplied in unlimited quanti-

ties and there were no disturbing currents to put out or interfere with the work

60 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

of the burners, steam could be supplied at a sufficient pressure to run the en-
eines. It was realized, however, that the conditions in flight would be very dif-
ferent, and that in order to protect the apparatus from the wind, some sort of
protecting covering would have to be devised, which would of itself introduce
new difficulties in providing the burners with a proper and uniform draft.

The hull, as at first constructed, consisted of a cylindrical sheathing open in
front, through the rear end of which the boiler and aeolipile projected inward,

Fic. 10. Diagram of pendulum.

so that the air taken in at the front would be drawn through the boiler and hearth
to the exclusion of lateral currents. In the first tests, however, after the hull had
been applied, it was impossible to secure a proper rate of combustion, nearly the
whole hull being filled with a bluish flame, while only a very small portion of the
eases of combustion passed into the coils of the boiler. The remedy for this lay in
obtaining an increased draft, and a small stack was, therefore, arranged to carry
off the products of combustion. This proved inadequate, and it was only after
several weeks of experiment with various types of smoke-stack, and constant
alteration of the aeolipile, that it was possible to make the apparatus work effi-

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 61

ciently when it was inside the hull. Finally such a degree of success was attained
that the burners could be kept lighted even when the aerodrome was placed in a
considerable artificial breeze, created by a blower in the shop.

In connection with these tests of the engines and boilers, some method was
desired, in addition to the Prony brake tests, by which the thrust of the propel-
lers when driven by the engines at various speeds could be measured accurately
and in terms which would be readily available in judging whether the aerodromes
were ready to be given an actual trial in free flight. Such a method was found

> which was introduced

in the use of an apparatus known as the ‘‘ pendulum,’
near the end of 1892, but was not generally used until the end of 1893. After
this time, however, this test was made a condition prerequisite to taking any of
the aerodromes into the field, and proved of the greatest assistance in estimat-
ing the probable outcome of the trials.

The apparatus used, which is diagrammatically shown in Fig. 10, was ex-
tremely simple both in theory and operation. It consisted primarily of a hori-
zontal arm AC carrving the knife-edge B by which it is pivoted on each side on
supporting beams not shown. Depending from AC is the light vertical arm DE,
rigidly joined to it and carrying the lower horizontal arm #G, all of which are
braced together so as to maintain the arm DE constantly perpendicular to AC.
To this arm FG the model was rigidly attached with its center of gravity in line
with the vertical arm DE and its weight mereased by the addition of properly
disposed flat weights, in order to make the angle of lift for a given thrust of the
propellers smaller and less likely to interfere with the working of the boiler and
separator.

Before the actual test of the ‘‘ lift ’’ could be made, it was necessary to know
the exact distance of the vertical center of gravity of the model and the extra
weights from the knife-edge B. This was determined by the following method:
A known weight was suspended from the arm AB at some arbitrarily selected
distance from the point B. This weight caused the perpendicular arms AB and
DE to rotate through an angle, @, which was measured on the scale KL. Know-
ing, then, the weight on the arm AB, its point of application, the weight of the
aerodrome suspended on the arm DE, and the angle of rotation, it is easy, by a
simple application of trigonometric functions, to determine the distance of the
center of gravity of the model from the point B.

In a test of Aerodrome No. 6 made on September 23, 1898, the weight sus-
pended from AB was 10,000 grammes, its point of application 50 em., the model
was weighted to 20,450 grammes, and the angle of rotation, 6, was 7° 2’.. Letting
y equal the distance of the CG from B, we may equate the balanced forces thus:

10,000 x 50 cos 7° 2’=20,450 x y sin 7° 2’
10,000 x 50 cot 7° 2’=20,450 y
y=198.2 cm.

62 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 21

Having determined this distance, the weight on 46 was removed and the,
aerodrome was allowed to regain its former position. The distance of the center
of thrust from PB was then measured. The engine was next started and the num-
ber of revolutions of the propellers counted by a tachometer. The thrust of the
propellers, acting perpendicularly to the arm BD, produced rotation around the
point B, the angle of which was measured as above.

In the power test of No. 6, the following data were obtained:

W=weight of aerodrome=20,450 grammes.

é6=anele of lift=19° 30’.

Distance of CG from center of rotation=198.2 em.”

Distance of center of thrust from center of rotation=186.3 em.

As the propeller thrust and the weight of the model are forces acting in opposite
directions at known distances from a center of rotation, letting L equal the ‘‘dead
lift,’? we may express the equation thus:
W sin 0X198.2=L x 186.3,
198.2
e633
L=7,263 grammes ‘‘ dead lift.’’

x sin 19° 30’ x 20,450,

The flying weight of Aerodrome No. 6 was 12,064 grammes, and the per cent of
this weight lifted was, therefore,
7,268
12,064

This was much more than was necessary for flight, but in order to insure

= 60.3.

successful flights and avoid delay, the rule was made in 1895 that no aerodrome
was to be launched until it had previously demonstrated its ability to generate
enough power to maintain for at least two minutes a lift of 50 per cent of the
total flying weight. At the same time other important data were obtained, such
as the steam-pressure, the time required to raise sufficient steam, the total time
of the run, and the general working of-the boilers and engines.

As will easily be seen, these tests afforded a most satisfactory basis of judg-
ing what the aerodromes might be expected to do in actual flight if the balancmg
were correct.

At this time, October, 1893, the aerodrome (Old No. 4) was practically
complete, and the most anxious thought was given to lightening it in every way
consistent with the ever-present demand for more power, which necessitated an
increase in the weight of both burners and boilers to supply the requisite steam.

On November 14, when the aerodrome was prepared to be shipped to Quan-
tico for trial, its condition was about as follows. The steam-generating appa-
ratus—the parts of which were of substantially the forms last described, al-
though some slight improvements had been introduced—had been developed to

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 63

such a point that a pressure of from 70 to 80 pounds of steam could be main-
tained for 70 seconds, when it was tested in the shop. What it would do under
the unfavorable conditions imposed by flight was to be learned only by trial.

At this pressure, the engines, the efficiency of which had been increased by
an improvement in packing, would develop approximately 0.4 indicated H. P., .
while at 105 pounds pressure they at times developed as much as 0.8 H. P.
When the aerodrome was tested on the pendulum, these engines, when making
less than 700 revolutions per minute, lifted over 40 per cent of the total flying
weight.

The propellers used at this time were accurate helices, having a diameter of
60 em., a width of blade of approximately 36 degrees, and a pitch-ratio of 1.25.
They were formed of wood, and were bushed with brass where they were at:
tached to the shafts.

AERODROME OLD NO. 4 AS PREPARED FOR FLIGHT BEFORE BEING SHIPPED FOR TRIAL
ON NOVEMBER 14, 1893

Part Copper |Stecl} Brass. | Iron Wood and| Mica and | Fluia Total and mean
; mobi : at : silk. asbestos. | i weights.
| ia = \~ 2S | 7 ar
gis. gms. gms. | gms. gms. gms. gms. | gms.
AG ONIPLE Te yeiajein ee «ale ni 200 os 92 ae oe 30 an 292
ICM en sooousdosenaooees 350 nc 57 ae ar ane So 387
Separator and pumps.... 300 30. 100 20 od do 50 450
Engine and frame...... a 350 570 ae 50 B5 28 920
Midrod (200¢em. long)... . 26 220 36 Ss 50 is Le 220
Two smoke-stacks ...... 70 a 6 ve O16 = so 70
Asbestos jacketing...... “ye 5 35 30 56 50 a 50
PAWTICHVEAD Cle -yeta crore -retsas= Oc se 56 82 a a6 ae 82
Spider between boiler and
REDON erates alelel cy osaisiate 52 >| BY)
NGAISERVAlVe.r:c csv ob ccere| 50 a5 15 15
To eely ene aed cs 952 | 600 814 | 102 cal mle 00 2518 5.54 Ibs.
52 eee eee ee BOM lee Bove ace sf 25 | 125
Pins foristarter cc. << 15 ao aD 15
Two large wings and tail. ne oi 55 o 571 Ne -+ | 571
Buffer and steerer....... Se .. comet n note 53 53
Lid doy Veg GODOOORDO SDE | os 5 =f “2 250 250
Rotalyen SUEY aay ace | 50 | 15 50 874 25 1014= 2.23 Ibs.
— ed _ - —_ ——_—.
Grand total........... 1002 615 864 102 874 75 3532—) 7.77 lbs.
Dausityse orate necs ss BAG |vsBer| 8.580025 0.8 3.0 are us
Volume (cu. ems.)...... . 113 79 102 | 136 1092 25 on 1425=) 87 cu.ins.
ALCON OLprcemcteratocientasicc ve oe 52) aie 30 un 100 100
WEI capo odoscdecandse Bo a5 he oc 50 on | 500 500
AUCH WSrinncoaadee aces Be op alle 1 lbs
5 125
WDA? Saciinessenaooaas . os oe a5 a oe me 500 f 2.01 ( II
Volume (cu. ems.)....... 46 aa ee sis 50 ae 55 2050
Permanent air spaces:
in midrod, vol. = 355 ee.
in engine frame, vol. = 100 ec. f 4132 7
volume as perII. 2050 cc. Deusity= 5-95 =1.65 } III
| ee

2505 ec.

64 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vot. 2

The total flying weight of Old No. 4, including fuel and water, was 4132
grammes (9.1 lbs.), a much larger weight than had been contemplated when
the original designs were made. A detailed statement of the weights of the
various parts of the aerodrome, together with some data as to its density, is
given on the preceding page. There were provided in the wings and tail ap-
proximately 2 sq. ft. of supporting surface to the pound of weight, which would
have been barely sufficient to sustain the aerodrome, even if it had been success-
fully launched and the wings had been built much stronger than the flimsy con-
struction in use at this time.

An air chamber, which served the double purpose of floating the aerodrome
and of providing a moveable weight by which the center of gravity could be
shifted to the proper position relatively to the center of pressuré, was con-
structed of the thinnest sheet-iron and attached to the midrod.

This aerodrome, the fifth in actual construction, and the first, after years of
experiment, to be carried into the field, was transported to Quantico, where the
first trial with it was made on November 20, under the conditions described in
Chapter IX.

1894

The aerodrome, No. 4, which has just been described, had not been put to the
test of an actual flight, for reasons connected with the difficulties of launching,
which are more fully described elsewhere; but, when the completed machine was
more fully studied in connection with the unfavorable conditions which it was
seen would be imposed on it in trials in the open air, many possibilities for im-
provement presented themselves. It was seen, for instance, that a better design
might be made, in which the engines, boiler and aeolipile might be placed so that
the center of gravity of each would lie in the same vertical plane as the central
line of the aerodrome. In order to do this the construction of a single midrod,
which was the distinguishing feature of Old No. 4, had to be essentially departed
from, the midrod of this new one, No. 5, being opened out into two rods, so to
speak, which were bent out so that the open space between them furnished a
sufficiently large hull space to hold the entire power generating apparatus. In
arranging the machinery within this hull, it was provided that, as the water and
fuel were expended, the center of gravity of the aerodrome would shift little,
and, if at all, backward relatively to the center of pressure.

Instead of the two small engines, which it will be remembered were mounted
on the cross-frame in No. 4, a single engine with a larger cylinder, having a di-
ameter of 3.3 em. (1.3 in.) and a stroke of 7 em. (2.76 in.), capable of developing
about 1 H. P. was used. This engine was mounted within the hull near the for-
ward end and drove the propellers by suitable gearing.

Se Sr Ge pene ee. ee eee ee ne

ee

> Sr es

ee

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 65

In addition to these radical changes many important improvements were
made in the different parts. Internal compartments were built in the separa-
tor, so that even if the water was displaced by the pitching of the aerodrome, it
could still perform its functions properly The pump was provided with a ratchet,
so that it could be worked by hand after the burners were lighted, and before
enough steam had been raised to enable the engine to run it. An active cireu-
lation was thus maintained in the coils of the boiler as soon as the burner was
lighted and before the engine was started, which prevented the tubing from be-
ing burnt out, as had frequently happened previously. The wing construction
was also improved and many other changes were introduced, which will be treated
separately.

In the meantime, No. 4, which had been damaged in the attempted launching
in November, 1893, was strengthened and prepared for another trial which took
place in January, 1894.

By the end of the first week in February, the engine of No. 5 was ready for
trial, and with a boiler pressure of about 80 pounds per square inch, apparently
developed 0.56 H. P. on the Prony brake, when making 800 revolutions per min-
ute. To accomplish this called for such good distribution of steam in the cyl-
inder, that it is doubtful if the power could be exceeded at that speed and
pressure.

It was, however, apparent that it was desirable to have a boiler capable of
supplying steam for at least one horse-power, and that in order to do this, there
must be an improvement in the aeolipiles. The problem consisted in arranging
to evaporate more than 500 cu. em., and in fact as nearly as possible 1000 cu.
em. (61 cu. in.) of water per minute, and, since from 200 to 300 cu. em. per
minute had already been evaporated, this was not regarded as impossible of ac-
complishment. The theoretical advantages of gasoline had for a long time been
recognized, as well as the very practical advantage possessed by it of keeping
lighted in a breeze, and several attempts had been made during the latter part
of the previous year to construct a suitable burner for use with it. These had
not been very successful; but in view of the increasing demand for a flame of
greater efficiency than that of the alcohol aeolipiles, it was decided to resume the
experiments with it.

Accordingly, a gasoline evaporator was tried, consisting in the first ex-
periment of a gasoline tank with nine flues, through which steam was passed.
A flow of steam gave a rapid evaporation of gasoline when the pressure did not
exceed 5 pounds. The chief difficulty with the burner employed was that the
supply of gasoline gas would rise and fall as the steam rose and fell, conditions
just the opposite of what was really desired. On the other hand, it was thought

that this gasoline tank would form a real condenser for the steam, so that a por-
6

66 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

tion of the exhaust steam would be condensed and be available for use in the
boiler again. The gasoline vapor had many advantages over the alcohol; but it
was at first possible to evaporate only 120 cu. em. of gasoline in a minute.

In the experiments that were made at this time (March 9) with gasoline,
the main object in view was to obtain a smooth blue flame at 10 pounds pressure.
There had been failures to accomplish this, owing to the high boiling point of
the liquid, and while the work was in progress it was still evident that the prob-
lem of the boiler and the flame which was to heat it had not been solved. A Prony
brake test gave, at 130 pounds pressure, 1.1 H. P. with about 1000 revolutions
of the propellers; but this was with steam supplied from the boiler of the sta-
tionary shop engine.

On April 1, 1894, the following record was made of the condition of Aero-
drome No. 5:

‘¢ The wings, the tail, and the two 80cm. propellers, as well as the two smaller
propellers, are ready. The cylinders, gear, pump, and every essential of the
running gear, are in place. The boilers, separators, and adjuncts are still under
experiment, but may be hoped to be ready in afew days. At present, the boilers
give from 450 to 600 grammes of mixed steam and water per minute. With 130
pounds of steam, the engine has actually developed at the brake, without cut-
off, considerably more than 1 H. P., so that it may be confidently considered that
at 150 pounds, with cut-off, it will give at least 0.8 H. P., if it works proportion-
ately well.’’

The delays incident to the accomplishment of the work in hand were always
greater than anticipated, as is instanced by the fact that it was the latter part
of September before the work was actually completed. The greater part of this
delay was due to the necessity for a constant series of experiments during the
spring and summer to determine the power that it was possible to obtain with
the various styles of boilers, aeolipiles, and gasoline burners.

While No. 5 was thus under construction, new and somewhat larger engines
had been built for No. 4, the work on them having been begun in January. The
cylinders of these engines, which are more fully described in connection with
Aerodrome No. 6, were 2.8 em. in diameter, with a 5 em. stroke, each cylinder
thus having a capacity of 30.8 cu. em., which was an increase of 36 per cent
over that of the old brass cylinder engines, which had previously been used on
No. 4. On April 28, under a pressure of 70 pounds, these engines drove the
two 60 em. propellers at a rate of 900 R. P. M., and lifted on the pendulum nearly
40 per cent of the total flying weight of Aerodrome No. 4, which was now ap-
proximately 5 kilos. A trial was made at Quantico in the latter part of May,
which is. described in Chapter IX. It is only necessary to mention in this con-
nection that there was a great deal of trouble experienced with the alcohol aeo-
lipile, the flame being extinguished in the moderate wind to which the aero-

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 67

drome was subjected while preparations for the launch were being made. More-
over the flame was so nearly invisible in the sunlight that it was uncertain
whether it was burning in the critical instants just before the launch, when doubt
might be fatal. These conditions resulted in a final decision in favor of gaso-
line, on account of its greater inflammability, and in the provision of such hull
covering that the fires could be lighted and maintained in a breeze.

In June, I tried a modification of the burner, in which the gasoline was de-
livered under the pressure of air to the evaporating coil. In the first trial steam
was raised to a final pressure of about 70 pounds, and a run of 45 seconds was
secured under a pressure of 40 pounds in the gasoline tank, which was thought
to be altogether too high; for, at the end of the run, the whole apparatus was
enveloped in flames, because of the gasoline that was projected through the
burner-tips.

Continual experiments with different forms of burner, illustrated in Plate
12, occupied the time, with delays and imperfect results, which were trying to the
investigator, but are omitted as of little interest to the reader. They had, how-
ever, the incidental result of proving the practical superiority of gasoline over
alcohol, and culminated in the evolution of the burner that was finally used
successfully. It consisted of a tank for the gasoline, from which compressed
air delivered the liquid to a small coil surrounded by asbestos, in which it was
vaporized. At the rear end of this coil three pipes were led off, one of which
was a small ‘‘ bleeder,’’ which fed the burner for heating the gasoline, the other
two leading to the main burners. After the generation of gas in the small coil
had been started, the heat from the small burner was expected to continue the
vaporization, so that nothing but gas would be able to reach the main burners.
A device was also introduced, which had greatly increased the amount and uni-
formity of the draft and consequently made the burners and boilers more effi-
cient than before. This consisted simply in passing the exhaust steam from the
engines into the smoke-stack, and it is remarkable that it was not thought of
earlier.

By the middle of September, 1894, both aerodromes were completed and
ready for another test. On September 27 the condition of Aerodrome No. 4
was as follows: The general type of construction, namely, that of a single
midrod, to which all the steam generating apparatus was attached, and which
supported also the cross-frame and the wings, was the same as in the construc-
tion of 1893. On account of the increased weight of the model, and the substi-
tution of an inferior piece of tubing in place of the former midrod, it was found
necessary to stiffen it by the use of temporary trusses. Permanent bearing
points for holding the aerodrome securely to the newly devised launching appa-
ratus were also attached to this midrod.

68 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

The engines in use at this time were the small steel cylinders described
above, which were mounted on the cross-frame, and drove the propellers directly.
These engines were capable of delivering to the propellers, as had been proved
by repeated tests, at least 0.66 brake horse-power.

The boiler consisted of two inner coils and an enveloping outer coil, loosely
wound and connected in series. The inner coils, each of which had about 17
turns of 8 mm. diameter, 0.2 mm. thick tubing, developed about 80 per cent of
the steam; the outer coil of 8 turns, while not exactly useless as a steam gener-
ator, afforded an efficient means of fastening the smoke-stack and cover of the
boiler, and for attaching the latter to the midrod. This boiler was externally
30 em. long, 16 em. wide, and 10 em. deep, weighing with its cover approximately
650 grammes. The stack for the burnt gases, into which exhaust steam was led
from a central jet, was about 1 foot long. At best this boiler was capable of
developing slightly over 100 pounds of steam.

The separator was of the form last described, except that the steam dome
had been moved toward the front, to prevent the jerk of the launching car in
starting from causing water to be pitched over into the engines. It was con-
structed of sheet aluminum-bronze, and weighed, together with its pump, 580
grammes. The pump, which was double-acting and fitted with ball valves, was
capable of discharging 4.5 grammes of cold water per stroke, its efficiency being
only about one-half as great with hot water.

The gasoline burner, which had been finally adopted in place of the alcohol
aeolipiles, had now been perfected to the form in which it was finally used. Two
Bunsen burners of special construction were provided with gasoline gas by the
heat of an intermediate accessory burner, which played upon a coil to which all
three burners were connected. Gasoline was furnished from a tank made of
aluminum-bronze, under an air pressure of about 20 pounds, the fluid beg un-
der the control of a screw stop-cock. This tank, which was capable of holding
100 to 150 eu. em. of gasoline, weighed 180 grammes, and the burners with an
outer sheathing weighed 302 grammes.

It was caleulated that about 3300 eu. em. (201 eu. in.) of air space would be
required to float the aerodrome in water, and this was supplied by an air cham-
ber, having a capacity of 2700 cu. em. (165 cu. in.), which could be shifted to
adjust the longitudinal equilibrium of the aerodrome, and about 900 cu. em. (55
cu. in.) of space in the gasoline tank and the midrod. The reel and float, which
served to indicate the location of the aerodrome, if for any reason it should be
submerged, were in one piece, and so moored that there was no danger of fouling
the propellers.

The total weight of the aerodrome was about 6 kilogrammes (13.2 Ibs.), or,
with a maximum quantity of fuel (850 eu. em. of water, 150 cu. cm. of gasoline),

eee, ee

7. aes 2

hy

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 69

less than 7 kilogrammes. From 60 to 90 pounds of steam could be maintained
by the boilers for about 2 minutes, at which pressure the engines developed about
0.66 brake horse-power, driving the 70 em., 1.25 pitch-ratio propellers at 700 R.
P. M., and giving a lift of from 2.6 to 3.0 kilos (5.7 to 6.6 pounds), or about 40
per cent of the flying weight.

The wings and tail had a total surface of 2.62 sq. m. (28.2 sq. ft.), giving :
ratio of 2.7 kilos to 1 sq. m. of wing surface (1.8 sq. ft. per pound). If the hull
resistance be neglected, the soaring speed of this aerodrome was about 5.9 metres
(19 feet) per second, or 13 miles per hour.

Turning now to the completed No. 5, its frame was of the

3

“¢ double mid-

rod ’’ type described above, the two tubes which formed the frame being pro-
longed at the front and rear to afford points of attachment for the wings and
tail. The range through which the wings could be shifted to adjust the position
of the center of pressure was, however, very small. The hull, which, it will be
remembered, contained all the power generating apparatus, was much stronger
and heavier than that of No. 4, and resembled somewhat the hull of a ship. It
had a frame-work of steel tubing brazed to the midrod, to which an outer
sheathing of sheet aluminum 0.3 mm. thick was attached. It was, however, ex-
cessively heavy, weighing nearly 800 grammes.

The engine, which was mounted near the front of the hull, was the single
cylinder, one horse-power engine, described above, which drove the two propel-
lers by suitable gearing. The remaining parts of the power plant were identical
with those already described in connection with No. 4, but the more advantage-
ous location of them in No. 5 rendered them somewhat more efficient.

It had been planned to use 80 em. propellers of 1.25 pitch-ratio on No. 5, but
it was found in the shop tests of the aerodrome that the cross-frame was not
strong enough to withstand the strains, and that the engine could be made to
work much more steadily with a smaller propeller. Accordingly, propellers of
70 em. diameter and 1.25 pitch-ratio, similar to those used on No. 4, were finally
substituted.

For floating the aerodrome, when it descended into the water, an air-cham-
ber similar to that of No. 4, but of a larger capacity was provided. With this in
place on the aerodrome, it was calculated that, if all the parts except this float
and the gasoline tank were filled with water, there would still be a buoyancy of
over 2 kilogrammes.

The total weight of No. 5 was 8200 grammes, or with its full supply of fuel
and water 9200 grammes. In this aerodrome the same boilers used in No. 4
were capable of maintaining for at least a minute 115 pounds of steam, so that
the engine now gave the maximum of one brake horse-power for which it was
designed, and, driving the 70 em. propellers, lifted repeatedly nearly 45 per cent

of the flying weight.

70 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 2

The wings and tail constructed for No. 5 were identical with those of No. 4,
being slightly curved and containing 2.62 sq. m. (28.2 sq. ft.), equivalent to 1.4
sq. ft. to the pound, which with the flimsy construction of the wings gave an en-
tirely inadequate support to the aerodrome.

During the summer a launching apparatus of a new and improved type,
which is described in Chapter X, had been perfected, and with it repeated tests
were made of both aerodromes in October, November, and December, with the un-
satisfactory results recorded in Chapter IX. In the course of these experiments,
many slight modifications of the burners and boilers were made, but no important
changes were introduced except that the cross-frame of No. 5 was enlarged and
strengthened so as to admit of its carrying one metre propellers safely. The
results, however, which were obtained, did not compensate for the increased
weight of the larger frame.

Viewing the work of this year from the standpoint of results obtained in
the numerous attempts at flight, it would seem that very little progress had been
made, and that there was small reason to expect to achieve final success. How-
ever, if the work be examined more particularly, it will be seen that two of the
most difficult problems had been solved, one completely as far as the models
were concerned, and the other to a very satisfactory degree. First, a launching
apparatus, with which it was possible to give the aerodrome any desired initial
velocity, had been devised, and so far perfected that no trouble was ever expe-
rienced with it in testing the models. Second, as a result of the extended and
systematic series of experiments, which had been conducted under the direction
of Dr. Barus, a steam pressure of 115 pounds could be maintained steadily in
the boilers for at least a minute, and the burners could be kept lighted even in
a considerable breeze.

A summary of these experiments, together with some account of the diffi-
culties encountered and the results finally obtained with the apparatus in use
at the end of the year, is given in the following report, which was prepared by
Dr. Barus in December, 1894.

‘“« Tf water be sprayed upon a surface kept in a permanent state of ignition,
any quantity of steam might be generated per time unit. Similarly advantage-
ous conditions would be given if threads of water could be passed through a
flame. In practice this method would encounter two serious difficulties, the im-
portance of which is accentuated when the boiler apparatus is to be kept within
the degree of lightness essential in aerodromics. These difficulties are (1) the
danger of chilling the flame below the point of ignition or of combustion of the
gases, and (2) the practical impossibility of maintaining threads of water in
the flame. For it is clear that the threads must be joined in multiple are, so
as to allow a large bulk of water to circulate through the boiler, whereas even
when there are but two independent passages for the water through the furnace,
it is hard to keep both supplied with liquid without unduly straining the pump.
If the water be even slightly deficient, circumstances will arise in which one of

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 71

the passages is better than the other. This conduit will then generate more steam
and drive the water under force through the other passage, increasing the tem-
perature discrepancy between them. Eventually the hot passage reaches igni-
tion and either bursts or melts. This is what sooner or later takes place in
boilers adapted for flying machines and consisting of tubes joined in multiple
arc, when a single moderately strong circulating pump supplies the system.

““To avoid these annoyances, i. e., to increase the length of life of the
boiler, the boiler tubes are joined in series to the effect that a single current of
water may flow successively through all of them. It is needful therefore to
select wide tubes, such as will admit of an easy circulation in consideration of the
length of tubing employed without straining the pump and at the same time to
allow sufficient room for the efflux of steam. Other considerations enter here,
the bearing of which will be seen presently: if the tube be too wide the difficulty
of coiling it on a mandrel of small diameter is increased, while at the same time
the tube loses strength (cet. par.) in virtue of the increased width.

Diagram 2.

Diagram 1.

Fig. 11.

‘¢Tt is from considerations such as these that, in the course of many ex-
periments, copper tubing about 8 mm. in diameter has been adopted. Copper is
selected because of its freedom from internal corrosion, easy coiling, and be-
cause of its availability in the market. The thinnest tube to be had (walls only
0.1 mm. thick) will withstand more pressure than can be entrusted to the larger
steam receivers in cireuit with the boiler. The boiler weight is thus a negligible
factor, and it is quite feasible to reduce the thickness of boiler tubing, by the
superficial application of moderately strong nitric acid, to 200-400 grammes per
horse-power of steam supplied. External corrosion due to flames occurs only in
ease of deficient water, and if the boiler be made of tubing with the walls 0.2
mm. thick, it is in view of the possibility of such accidents. Boilers may then
be tested to 25 atm. without endangering the metal.

“‘ Boilers are wound or coiled with regard to the two points above suggested,
viz.: to avoid chilling the flame the successive turns are spaced on all sides, and
to bring the water as nearly into the flame as possible, the diameter of the coils
is chosen as small as expedient. Further reasons for this will presently be ad-
duced. The type of boiler eventually adopted is shown in the accompanying dia-
grams, | and 2, Fig. 11.

‘‘ Diagram 1, is a perspective diagram showing the plan of winding and Dia-
gram 2, an end view. The circulation is indicated. There are two inner coils

72 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

each containing about 17 turns, wound on a mandrel 5 em. in diameter. The turns
are spaced so as to allow about 1 em. clear between successive turns. The outer
coil envelopes both, and in this there are about 3 em. between successive turns,
and 8 turns in all. Length, say, 30 em., breadth 16 cm., thickness 10 em., give
the external dimensions of the boiler. The shell space between outer and inner
layers of tubing must nowhere be less than 1 em. When so wound, the inner
coils (here as in other boiler forms) raise about 80 per cent or more of the steam ;
the outer or enveloping coil, while not quite useless, make the most effective
frame work for the boiler jacket which has been devised. The coils are brazed
together by blind tubes, as shown in Diagram 2, to keep the whole in shape.
Weight with couplings and cover when complete 535 grammes.

‘« The cover is preferably of mica, through which the flame within the boiler
may be seen, and in which lightness, nonconduction, and resistance to the disin-
tegrating effects of high temperature are met with in a pronounced degree. This
jacket is held down by copper bands and the end band is continuous with the
long smoke-stack, as will presently be shown.

‘“*The wide form of boiler with two coils within the envelope is not abso-
lutely essential. The same amount of steam can be generated from one coil in
an envelope in other respects equal to Diagram 1 if a sufficiently hot flame be
passed axially through the coils. Such a flame, however, is unstable, and for
this reason two milder flames with a good air access are to be preferred on prac-
tical grounds even if the weight is thereby increased.

“To further understand the boiler construction it is advisable to consider
the action of the flame. Inasmuch as wide tubes must be used, the problem of
evaporating water as fast as possible is equivalent to getting heat into the cur-
rent (water and steam circulating through the coils) as fast as possible from
without. If, therefore, ¢ is the mean temperature of the fluids within the coils,
and 7 the effective temperature surrounding the tube, then the rate at which
heat will flow into the tubes is proportional to 7—t. Now t the temperature of
the steam is nearly constant (100°-150°) whereas 7 the effective flame tempera-
ture may vary from 800° to, say, 1600°. It is for this reason that the heat
sponged up by the boiler depends almost directly on the flame temperature.

‘* What conditions, therefore, will make the flame effectively hot?

**(1) The coils must obviously be brought as nearly into the flame as feasi-
ble: for this purpose the cylindrical helix is better than any other form. But

“«(2) The turns and coils must not be so crowded together as to chill the
flame into imperfect combustion in various parts of its extent. Hence the loose
form of winding. Again

“*(3) There must be oxygen enough to allow complete combustion, and

‘*(4) The flame itself must be hot and the radiation checked by good
jacketing.

‘*To take up the last points: the effective heat of the flame depends not
only on the combustion heat of the fuel used; it depends also, among other things,
on the speed with which this combustion takes place. A flame burning from a
low pressure of alcohol.gas will be at low temperature as compared with a flame
burning from high pressures of the gas. If the flame be burnt from a Bunsen
burner in the usual way it is an interesting question to know how flame tempera-
ture will vary with gas pressure. At present we know it merely in steam pres-
sures incidently produced in a given engine (No. 4) as for instance:

Flame pressure, 10 Ibs., 20 Ibs., 30 Ibs. the gt peer
Steam pressure, 40 Ibs., 80 Ibs., 120 Ibs. {~~ picearamnrcy Nic

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‘‘ Unfortunately there is a limit set to this process of increasing the steam
supply, quite aside from conditions inherent in the method. This is due to the
fact that a certain speed of efflux cannot be exceeded without putting the flame
out. Suppose, for instance, in Fig. 12, that a gas generated from a liquid is
ignited at the end of the Bunsen burner I’; then if the velocity of efflux of mixed

A B
—

Fig. 12.

gas and air in the direction AB from the mouth of F exceeds the velocity of com-
bustion in the direction BA, the flame will obviously be carried away from the
mouth of the tube and dissipated. This state of things is actually realized at
pressures exceeding about 15 Ibs., depending on the degree of mixture of the com-
bustible gases used, and therefore on apparently haphazard conditions connected
with the jet, the air holes, the air supply, ete.

Fig. 13.

‘< Tf, however, the velocity of the jet at the point of efflux be checked by an
obstruction like a cylinder C, Fig. 13, placed co-axially with the burner tube F’,
the speed of combustion will no longer be exceeded (supposing C properly chosen)
and flames will then burn from high-pressure gas. In this way flames were
maintained generated from alcohol gas at even 40 Ibs. and above.

Lee
Shsc
Fig. 14.

‘©The gas escaping from the Bunsen burner is never sufficiently aérated to
burn completely. Otherwise there would (in general) be explosions in the tube
F. A part of this air is supplied at the mouth of the boiler B, Fig. 14, and the
amount available here will depend on the velocity of the jet ”. Hence it does
not follow that a high-pressure burner like that in Fig. 11 will supply a pro-
portionate amount of heat, since its jet suction is not intense and the combustion
within the boiler is incomplete. This difficulty may be remedied by placing

74 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

air holes in the jacket of the boiler, provided the boiler be wrapped loosely
enough not to chill the flame below ignition. It is with reference to this effect
that the boilers, Fig. 11, were wound. A number of rifts aaa, Fig. 15, are then
left in the jacket through which air may enter in virtue of the burner flame act-
ing as a jet at the mouth of the boiler.

‘‘ When so constructed the flame at first enters the inner coil only; but after
a little while it suddenly spreads out throughout the whole interior space and
enyelops the coils. This sudden expansion is due, probably, to the assumption
of the spheroidal state by the water within the coils, the current now flaring on
an enveloping cushion of steam. The pump must work well, for deficient water
means a hot tube and deficient steam, or eventually a rupture of the tube.

‘“ Thus far the dependence for draft has been on the burner jet and the suc-
tion of the smoke-stack in virtue of the inertia of the moving gases. But even
with this ventilated boiler, this method is limited to certain dimensions of the
boiler. Thus a boiler 80 em. long yielded about the same quantity of steam as a
boiler half as long and otherwise similar. Only the initial parts of the boiler
are, therefore, relatively efficient, and the reason of this seems to be that, apart
from shape, ete., the flame as a heat-producing agent is practically defunct, when
a certain amount of heat has been taken out of it: in other words, even with

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fair ventilation the flame is eventually chilled off by the voluminous products of
combustion continually accumulating in the boiler. The same choking action ac-
companies the presence of unburnt gases. If, for instance, the flame be burnt
in the air, it is slender and much smaller in volume than in the boiler. The flame
is also of small volume and burns completely in a wide boiler, but the steam is
always deficient, because of the distance between flame and coils (see above).
With the above apparatus about } 1b. of dry steam per minute per square foot
of heating surface was attained.

‘¢Mhis introduces the final condition for rapid steam generation. There
must be artificial suction at the smoke-stack. By passing the exhaust steam in
the form of a central jet through the smoke-stack the yield of steam was increased
20 to 30 per cent. In fact as the supply of gas from the burner is given, the
artificial suction in question means more air in the boiler for the same amount
of eas and it means also a more rapid removal of the exhaust gases. The ex-
periments with steam suction are yet to be completed, and with them the boiler
question is to be finally laid at rest. The chief points at issue are these:

‘1. Seeing that the jet suction increases with the length of the smoke-stack,
up to a certain length at least, how long and how wide must the efficient smoke-
stack be made? Thus a smoke-stack 10 em. long is all but useless. Good re-
sults are obtained when the stack measures 30 em. in length beyond the end of
the steam jet.

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT

‘<9. What is the relative efficiency of the initial and final halves of the
length of the boiler? This will show in how far it is useful to increase the
length of the boiler for a given burner and steam jet. It will also show what
advantage is to be gained from triplicate boilers with three burners, as compared
with duplicate boilers with two burners, or single boilers with one burner, when
the same weight of tubing is used throughout.

‘¢ 3. What is the effect of pressure on the aeolipile tank, or in how far does
the steam generated depend on what may be called the pressure of the flame?
This is also an important point which remains for quantitative solution. It can
be approached in two ways: either by finding the steam evaporated in terms of
the tank pressure, or by finding the temperature of the flame pyrometrically.

‘4. What speed of water circulation best conduces to steam generation?
A good pump is now installed by which the circulation can be varied. If water
ean be put into the boiler just fast enough to come out dry steam at the other
end, the efficiency ought to be a maximum, but it does not follow that it will be
so, for one can imagine a wet circulation sponging up more heat than one which
is just dry at the end.’’

1895

During January and February, 1895, the experiments with boilers and burn-
ers were continued and even better and more uniform results than those given
above were obtained. The boilers of Aerodrome No. 5 were finally brought to
such a state of efficiency, that under favorable conditions a lift of nearly sixty
per cent of the flying weight was secured. This was much more than was re-
quired for flight, but it was decided to postpone the trials until No. 4 could also
be made ready for a test and the frame of No. 5 could itself be strengthened in
many weak places.

Upon examining No. 4, which had been put aside since the trials in De-
cember, it was found to have rusted so badly throughout and to be so unfit in
every way for trial, that a complete reconstruction of the whole would be neces-
sary. So many advantages had been gained in No. 5 by the double midrod type
of construction that it was decided to rebuild No. 4 on a modification of the same
plan, as shown in Plate 11, retaining, however, the same engines which had been
used before.

In this a very guarded return was made to the type which had proved so
unsatisfactory in No. 0, that is, making the hull support rods at the front and
rear for attaching the wings and tail. In this case, however, the hull was con-
structed very rigidly, and the tubes at the front and rear were firmly attached
and braced so that they could withstand a considerable strain without undue
distortion. The work on this frame was completed in March, but the other parts
were not in entirely efficient condition even in May, when the aerodromes were
taken to Quantico for trial. Moreover, it was found that the weight of this
aerodrome had increased far beyond the original estimates.

76 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

In view of the disasters from trials in the field, due to inability to obtain
automatic equilibrium in flight and to the flexure of the large wings rather than
to defects of the engines, the conditions at this time, after three years of failure,
seemed so nearly hopeless, that without abandoning the work on these steam
aerodromes, I again had recourse to the early plan of constructing smaller mod-
els driven by India rubber, in which the small wings employed could be made of
the requisite stiffness. Instead of employing twisted rubber, however, the de-
fects of which had been amply proved in previous trials, these new construc-
tions were meant to employ rubber directly stretched and pulling. In this con-
dition the rubber exercises nearly six times the power in proportion to weight
that it does when twisted, but on the other hand it requires a very strong frame
and subordinate parts.

I spent an inordinate amount of time and labor during this year in attempt-
ing to employ this latter form of construction and finally got a few useful re-
sults from it, but none in proportion to the labor expended.

During March, Aerodrome No. 5, the frame of which had proved on test to
be radically weak, was completely refinished except for the wings. The propel-
lers had hitherto been made of wood, but in May, I commenced a new construc-
tion of steel, wood and cloth, on a plan giving a figure which, though not rigor-
ously helicoidal, was practically near enough to the theoretical form and was
also both lighter and more elastic than the wooden construction.

On May 8 and June 7 Aerodrome No. 5 was again tried at Quantico,
and although the tests were unsuccessful, in that the aerodrome failed to fly,
partly because of the fact that so much time was spent in raising steam that prac-
tically the entire supply of fuel and water was exhausted before the aerodrome

vas actually launched, yet it had come so much nearer flying than any machine
had previously done, that it was felt that if either the power could be increased
or the weight decreased even a slight amount, the aerodrome would probably
fly. In view of the great care that had been exercised in keeping down the weight,
it seemed almost hopeless to attempt to reduce it, and it also seemed equally
hopeless to attempt to get more power without increasing the weight. How-
ever, something had to be done to increase the ratio of power to weight, and as
it was seen that this would involve extensive changes in No. 5, it was decided to
entirely rebuild No. 4 with this idea in view, though it was evident that it in-
volved a plan of construction even lighter than the dangerously light plan on
which No. 4 had already been constructed.

During Mr. Langley’s absence in Europe in the summer, Aerodrome No. 4
was entirely reconstructed and made to embody many new characteristics, the
changes introduced being so radical that this model was henceforth designated
as ‘* New No. 4.’’? The new characteristics of this model were its unprecedent-

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 77

edly light frame and the elevation of the transverse frame 12 centimeters above
the midrod, whereby the position of the line of thrust was raised so that it was
20 centimetres from the center of pressure, which from theory seemed to be
very nearly its correct position. The total flying weight was but 6400 grammes
(14 pounds), with a total supporting surface of fifty-four square feet, equivalent
to very nearly four square feet per pound. It was hoped that with this extremely
light construction the ‘‘ dead lift ’’ would amount to a large percentage of the
flying weight, and as much as sixty per cent was actually lifted on the pendulum.
As, however, the aerodrome approached completion it became more and more
evident that the construction was hopelessly fragile, the frame being scarcely
able to support itself in the shop. By November this conclusion became certain,
and this aerodrome (New No. 4) was never put to an actual test in the field. The
very expensive set of wings covered with gold beater’s skin, which were also
constructed at this time for this model, proved so weak under test that they were
entirely abandoned.

When Mr. Langley returned to Washington in the fall, many important
points, which had been under special consideration during the past year, partic-
ularly those relating to the disposition of sustaining surfaces, and the pro-
vision of automatic equilibrium, were still not definitely determined. It was
not yet decided whether two sets of wings of equal area should be used for the
aerodrome, or what the efficiency per unit of area of the following surfaces was
in comparison with the leading surfaces. To aid in determining these and other
important points concerning the relative position of the center of gravity and
the center of pressure in the horizontal planes, he had several small gliding mod-
els made, which could be used with either one or two pairs of wings, and afforded
an opportunity for testing and comparing several types of curved surfaces.

These models were built so that the center of gravity could be adjusted to
any desired point, and had in addition, as a means of assisting in preserving
equilibrium, a small tail-rudder, shaped somewhat like a child’s dart, which was
intended to support no part of the weight.

The tests with these models were very satisfactory and aided greatly in the
final development of what is known as the ‘‘ Langley type.’’ Indeed, in the
single month of November all the points, which had hitherto been more or less
indefinite, were finally decided upon, and the tests of the following spring proved
these decisions correct.

Two sets of wings of equal area were hereafter provided for every aero-
drome, which not only greatly increased the stability, but also overcame the
difficulty hitherto experienced in bringing the CP over the CG. The tail-rudder,
formed of planes intersecting at right angles, was adopted as the means of con-
trol. In use on the aerodromes it was set at a negative angle, and given a certain

78 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

degree of elasticity, which was at first provided in the frame of the rudder, but
was later given by a flat wooden spring, by which it was attached to the aero-
drome. The tail in this form now became the sole means of controlling the
equilibrium, and the results obtained with it were so very satisfactory that no
further attention was given either to the gyroscopic control built during the pre-
vious summer, or to any of the electrical forms of control constructed prior to
that time, all of which involved more or less delicate apparatus.

The definite form into which these ideas crystallized is perhaps best exem-
plified in the letter of instructions issued by Mr. Langley on November 30, 1895
to the men employed on the work. The text of this letter is given in the Ap-
pendix, and the forms referred to in it for recording the weights and adjust-
ments of the aerodromes are those used in the data sheets after this time.

In October work was resumed on Aerodrome No. 5, on which nothing had
been done since its test on June 7. The reconstruction of ‘‘ Old No. 4’ into
‘“ New No. 4’ which had occupied the entire summer, and the final result of
which was the production of a machine so radically weak as to be useless, had
been so discouraging that it seemed vain to attempt in any way to decrease
the weight of No. 5. The addition of the rear wings in place of the tail had,
however, so greatly increased the supporting surface that it seemed possible
that No. 5 might now be able to fly with no greater engine power than it had
on June 7. Some weak places in its frame were, therefore, strengthened and
the midrod at the front was raised five centimetres in order to raise the center
of pressure farther above the center of gravity and give the front wings a
ereater range of adjustment. Some slight changes were also made in the gear-
ing which drove the pump, so as to make it work faster, and new burners, boilers
and a gasoline tank were constructed during November. Later the midrod, which
had formerly consisted of two separate pieces attached at the front and rear
respectively of the main frame, was made continuous, and in order to avoid
passing it through the smoke-stack, the stack was made to fork at this point.
These changes are clearly shown in Plates 14 and 15, which are photographs taken
on December 3. This plan was, however, soon changed so that the midrod
passed through the smoke-stack and was rigidly attached to the frame at several
points, and a new pump and new boilers were substituted for those which had
been worn out. Aside from these changes, which although small, added very ma-
terially to the general strength of the frame, no important changes were made
in No. 5 prior to its remarkable flight of May 6, 1896.

While these changes were being made in No. 5, similar ones were also being
carried out in New No. 4, and the addition of the rear wings to No. 4, together
with other slight changes, made it such a distinctively different machine from
what it had been, that it was now designated as No. 6. After making extensive

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repairs to the extremely light frame of No. 6 (formerly New No. 4) it was
thought to be in suitable condition for flight and was accordingly boxed prepara-
tory to sending it to Quantico.

The year, therefore, closed with No. 6 apparently in condition for test, but
it was decided not to take it to Quantico until No. 5, which was still undergoing
repairs, could also be got ready.

1896

A few days after the beginning of the new year, while the repairs on No. 5
were being completed, it was decided that the frame of No. 6 which had been
boxed ready to be carried into the field for trial, was so weak that before putting
it to an actual test in flight it would be best to make some tests on the strength
of its frame. While testing the frame for torsional strength, it broke under the
moderate test of a weight of 500 grammes placed at the tips of the wings, the
angle of deflection just prior to its breaking being 35°, while the frame of Old
No. 4 in March, 1895, had shown a deflection of only 10.5° under a similar test.
This breaking of the frame showed very plainly that the worst fears in regard
to it had been realized and that by some means or other the frame must be
strengthened. This was finally accomplished by making the midrod continuous
through the smoke-stack as had already been done in No. 5, and at the same
time an additional improvement was made in the means of attaching the Pénaud
tail, whereby it was lowered in order to give it a greater clearance in passing
under the launching ear in actual test. Later the boilers proved defective and
new ones were substituted, but except for some minute details no further changes
were made in Aerodrome No. 6 prior to its test in May.

On May 6, No. 6 was unsuccessfully tried at Quantico just prior to the very
successful test of No. 5. In this test no serious damage was done to the frame,
but before going to Kurope in the summer, Mr. Langley ordered that both aero-
dromes be completely overhauled and put in condition for further experiments
in the fall. In this remodelling practically no changes were introduced in the
frame of either No. 5 or No. 6, but the engines of No. 6 were refitted and a new
boiler was substituted, which, with slight improvements in the burner, resulted
in a somewhat increased power in the engines.

A complete description, giving all essential details of both Aerodromes Nos.
5 and 6, will be found in Chapter X.

CHAPTER VIII

HISTORY OF CONSTRUCTION OF SUSTAINING AND GUIDING SUR-
FACES OF AERODROMES 4, 5 AND 6

INTRODUCTION

In some early experiments in 1887 with the small models without motor
power, which have not been particularly described, two pairs of wings, in the
same plane, were employed for reasons connected with stability. Afterward,
in many of the rubber-driven motor models, which have been described in Chap-
ter II, two large front wings were employed and the following pair were di-
minished into what may properly be called a tail. This plan was a retrogres-
sion in design, and it was pursued by the writer with a pertinacity which was
not justified by the results obtained, being used even on the early rubber-driven
models.

In this construction, it will be observed that the flat tail was in fact not
only a guiding but a sustaining surface, since it bore its own share of the
weight. It was not until a much later date (November, 1895) that the writer
returned to his earlier construction of two pairs of wings in the same plane
bearing the whole weight of the aerodrome, to which was now added a flat
tail, whose function was not to support, but wholly to guide. This was de-
veloped into the final construction by the addition of a vertical rudder or
rudders.

The present chapter is not concerned with the history of the earlier at-
tempts with small models, or of those numerous constructions of sustaiming sur-
faces which were never put to actual trial; nor does it give any description of
the experiments which were made in placing one set of surfaces over the other,
according to a method suggested in ‘‘ Experiments in Aerodynamics.’?*

The experiments in ‘‘ Aerodynamics,’’? and the theoretical considerations
given in Chapter V on sustaining surfaces, would never alone have led to the
construction which was finally reached, which was largely due to the hard les-
sons taught by incessant accident and failure in the field. The present chapter,
therefore, should be read in connection not only with the pages of ‘‘ Aerody-
namics,’’ but with Chapters V and IX of this book.

It is to be remembered that, while the center of gravity of the aerodrome
could be determined readily and exactly, the center of pressure could be de-
termined only approximately in advance of trial in actual flight. The positions

1 Chapter V.
80

; : 7
=
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;
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i
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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 16

oe

300 C.M.

Fig. A.

Fic. B

Fic. C.
= 300 C.M.

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Fre. D.
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t-I100

100 200 jis 400 500 C,M.

lo 1 | 1 Pex ae 2 ee Se ie es ee ee

EARLY TYPES OF WINGS AND SYSTEMS OF GUYING

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 81

of the supporting surfaces given in this chapter are, then, approximations made
from rules for ‘* balancing,’’ i. e., for obtaining equilibrium in actual flight,
rules which are in fact tentative, since they are founded on a priori consider-
ations with partial correction from the empirical knowledge gained by pre-

vious field trials. For these rules see Chapter VI.

1893

With reference to the supporting and guiding surfaces of Aerodromes Nos.
4, 5, and 6, Aerodrome No. 4, in its earliest condition mentioned in the preced-
ing chapter, was taken into the field, but never brought to trial in the air. It
is sufficient to say that in the largest of the three sets of wings constructed,
each wing was 17X51 inches, and therefore contained about six square feet, so
that with the tail (which was at this time a supporting surface), whose area
was one-half that of the two wings, the total supporting surface was 18 square
feet, or since the flying weight was 9.1 pounds, the proportion of surface to
weight was somewhat less than 2 square feet to the pound. The wings were at
this time ribless, it being expected that the silk cover which was purposely left
loose would take its curve from the air filling it, which subsequent experience
has shown would have led to certain disaster if the aerodrome had been launched.
It may be added that there was a vertical rudder of what is now seen to have
been a wholly inadequate size. These remarks may be applied with little modi-
fication to the attempted flight with No. 4 on May 25, except that the vertical

rudder had been made larger, but was still much too small.

1894

From the account of the field trials to be given in Chapter LX, it will be
seen that in numerous attempts at flight prior to October 6, 1894, the cause of
failure can in every instance be traced to imperfections more fundamental than
those of the sustaining surfaces, either the launching device or some other
part failmg to work satisfactorily. I therefore commence a description of the
sustaining surfaces with those of Nos. 4 and 5 as used on that day.

The construction of the wings of No. 4 and No. 5, which were nearly iden-
tical, is shown in Fig. A Plate 16. A rod of hickory, tapering from $ inch in di-
ameter at the larger end to + inch at the smaller, was steamed and bent, as
shown in the drawing, to form the main front rib of the wing. This was
firmly clamped to the midrod, and to the rib in turn were attached a number
of cross-ribs of hickory, slightly curved, the inner one of which was fastened
to the hull at its inner extremity, while the whole was covered with silk. The
length of each wing was 162 em. (63.75 inches), and the width 54 em. (21.25
inches). The tail was plane and equal in area to one of the wings, so that the
joint area of the wings and tail was 2.62 square metres (28.2 sq. ft.).

7

82 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

Each wing was attached to the midrod by a single clamp, different forms
of which are shown at Ff, G, H, I (Fig. 16). The clamp consisted of two short
split tubes, into which the main front ribs were securely clamped by means of
screws. They were set at an angle and united to a grooved frame, by which
the wings could be readily attached to a second piece clamped about the mid-
rod. The tail clamp, like the wing clamp, was composed of two pieces, sliding
one upon the other, but as the tail formed a single surface, one part was per-
manently attached to it. Clamps F, G were fitted to aerodrome No. 4, and H,
Ito No. 5. The wings were set at a diedral angle of about 150°, but as they were
not guyed in any way, this angle in flight and under the upward pressure of the
air probably became much less. The tail was plane but ribbed like the wings.

WING CLAMPS 1996

pees 7S " ce

be

1835

» ee
B

Fic. 16. Wing clamps, 1892-1896.

In preparing the machine for flight, the wings and tail of No. 4 were set
at a very small root angle with the midrod, perhaps not exceeding 3°, but while
this angle might be maintained at the firmly held root of the wing, it was later
seen to be probable that the extremity of the wing was flexed by the upward
pressure of the air after launching, though the full extent and evil effect of
this flexure was not recognized at the time. In the approximative calculations
for ‘* balance,’? made at this time, the tail was treated as bearing 4 of the weight
of the aerodrome, as it was } of the supporting area, for though it was recog-
nized that its position in the ‘‘ lee ’’ of the wings rendered it less efficient, the
degree of this diminution of efficiency was not realized. <A vertical rudder
20 em. x70 em. (8 in. x28 in.), with an area of 0.14 metres (1.5 sq. ft.) was used.

a

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 83

The particulars of the launch will be found in Chapter LX. In the present
connection, it is sufficient to say that though launched with the requisite veloc-
ity and without accident, it fell into the water at a distance of about 15 metres
(49 feet) with the midrod nearly horizontal, the combined effect of engines and
initial impulse having in fact kept it in the air for less than two seconds. The
true cause of this failure not then being recognized, it was attributed to the
angle of the wings with the midrod having been too small.

The launch of No. 5 followed almost immediately, but taking warning by
the supposed cause of failure of No. 4, its wings were set at a root angle of 20°,
and a hurried adjustment was made to secure greater rigidity, the tip being
partly secured against twisting by a light cross-piece, and guyed so that the
wing as a whole was not only at a greater angle, but stiffer than in the case of
No. 4. These changes it was hoped would cause the aerodrome to advance at
a considerable initial angle with the horizontal, and it did so, for instantly after
the launch, as the aerodrome escaped from its bonds into free air, the inclina-
tion of the midrod increased until it stood at about 60°, when the machine,
after struggling a moment to maintain itself, slid backward into the water
(with its engines working at full speed) after advancing about 12 metres (39
feet), and remaining in the air about 3 seconds.

On the whole, the result of the first actual trial of an aerodrome in the field
was disconcerting, for unless the result was due to the wings being placed in
a position wholly unfavorable to support, there seemed to be no doubt that
either the engine power or the supporting surface was insufficient. Now this
engine power was by computation between three and four times what was nec-
essary to support the aerodrome in horizontal flight at an angle of 20°, and
after making every allowance for slip, there should have been still an excess of
power for the first flight of No. 4, whereas actual trial indicated that it was
insufficient. But on the other hand, the experiment with No. 5, which moment-
arily held its position in the air at an angle of 60°, seemed to indicate that the
engine power was abundant, and that the failure must be traced to some other
cause.

As a result of these experiments it was concluded, ‘‘ that it is an all-im-
portant thing that the angle of the front wing shall be correct, and that this
cannot be caleulated unless it is known how much the tip will turn up under
pressure of the weight.’’ I felt, then, that I had learned something from the
failures as to the need of greater rigidity of the wings, though how to obtain
this without adding to their weight was a trying problem. It was thus at an
early stage suspected that the evil to be guarded against in wing construction
was the distortion of the form of the wing under pressure, chiefly by torsion,
which is specially hard to provide against without a construction which is nec-

84 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

essarily heavy. This suspicion was a correct one, though the full extent of the
evil was not yet surmised.

In the light of subsequent experiment it may now be confidently stated that
the trouble was with the wings, which at the moment after launching were flexed
wholly out of the shape which they were designed to have, and which they re-
tained up to that critical moment.

After returning to Washington, one of the wings was inverted, and a quan-
tity of sand, equal in weight to the pressure upon the wing in flight, was added,
under which the yielding at the tip amounted to 65°, or from +20° to —45°,
showing that the wings were entirely too weak to sustain the aerodrome.

In speaking of the efforts to strengthen the wings, it must be constantly
remembered that this could hardly be done in any way which did not involve
increased weight; that is, it could hardly be done at all, since increased weight
was forbidden.

The first attempt at systematic guying was made on October 27. As shown
in Fig. B, Plate 16, two guy-posts extending beneath the midrod were con-
nected by guy-wires with the outer extremities of the wing, by means of which
it was sought to hold the wing in place and prevent its extremity from twist-
ing upward, while a third wire connecting with the bowsprit prevented its mov-
ing backward. In addition, two aluminum wires, stretched across above from
wing to wing, kept the lower guys tight.

On October 27, Aerodrome No. 5, equipped with large new wings and tail,
having a combined area of 3.7 square metres (40 sq. ft.), the wings being each
64 em. x 192 em. (25.25 in. x 75.75 in.), turned sharply and completely round, ap-
parently through some internal current of the main wind against which it was
advancing. Owing to this almost instantaneous turn, it lost headway and came
down. This led to the subsequent construction and use of a much larger verti-
cal rudder, intended to prevent in future any such sudden pivoting and conse-
quent loss of momentum. The wings showed a tendency to ‘‘ pocket ’’* and
bag, which indicated some serious fault in their construction.

As a result of these experiments, it was decided on October 29 to attempt
to make the wings stiffer (though their weight was almost prohibitory), by in-
serting more cross-pieces, cross-pinning and guying them so as to make them
more rigid as a whole, and less liable to pocket.

At this time an automatic device in the form of a sliding tail was designed,
which it was thought would cause the center of pressure to move backward
when the aerodrome reared, and forward when it plunged downward, but the
device, though afterward constructed, was never brought to trial in the field.

Aerodrome No. 5, equipped with a new set of wings similar to those used

*“ Pocketing ” is a form of distortion in which the canvas or silk bags locally in numerous places
between the cross-ribs,

Ph eh eagetey

‘A ah

at

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 85

on October 27, and guyed as in the previous experiment, was again launched
on November 21, with the results recorded in Chapter IX. The failure was
attributed to the twisting of the wings under pressure to such an extent that
not only was their effective area greatly reduced, but the outer portions were
upturned so as to catch the air upon the upper surfaces, the result being in
part a downward pressure.

On the following day a pair of the wings was inverted and a weight of
sand equal to the air pressure to which they were subjected in flight, was dis-
tributed over their surfaces. Under the action of this, the twisting of the wing
was seen to increase from the root, which was held with comparative rigidity,
up to the tip, where in spite of the cross-ribs it amounted to 45°. The resist-
ance to torsion lay chiefly in the front rib, which, in addition, could be bent
easily, allowing the surface to become distorted with great loss of lifting power.

The experiments of 1894 had demonstrated the urgent necessity for greater
rigidity in the sustaining surfaces, which might, as it seemed, be obtained either
by increasing the strength of the framing (which meant additional weight) or
by resorting to some new and untried construction, or by a proper system of
guying. Guying seemingly offered the most feasible solution of the problem;
but although the system of wire guying was thoroughly tried, the result was
very unsatisfactory, as the wings continued to twist and bag in a way that was
extremely discouraging.

1895

I accordingly had recourse in 1895 to the system of wooden guy-sticks
shown in Fig. D, Plate 16, which necessarily added greatly to the weight of the sus-
taining surfaces. Hach wing was separately strengthened by means of a light
rod of spruce, in cross-section about the size of the main front rib, extending
across the upper surface of the wing, at a distance of about one-third the
width of the wing behind the front rib. It was tied to each of the ecross-ribs
and to the outer bent portion of the front rib, and at its root was fastened to
the frame of the aerodrome.

This effectually prevented the bending of the front rib and the consequent
bagging of the cover, and to that extent marked a decided advance in wing
construction. But it was faulty, in that, not being supplemented by wire euy-
ing, it offered little resistance to the twisting of the wing about the main front
rib, the rear tip of the wing being free to turn up under pressure, as it had
done on former occasions. A similar guy-stick was stretched across the tail. To
guard against torsion, rods extending diagonally across the wings and tail were
used, which, with the aid of the guy-sticks just described, prevented the surfaces
from twisting greatly. In addition, a rod joining the front ribs and stretching
across from wing to wing tended to maintain a fixed diedral angle.

86 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

The wings as thus guyed were rigid enough, and in the field-trials of No. 5
on May 8 and June 6, did not yield noticeably under pressure, and there seemed
to be no serious default in their lifting power, but the guy-sticks were heavy
and the system was not again employed. The wings used in these trials, shown
in Fig. C, Plate 16, had a frame of hickory, consisting of a front rib and nine cross-
ribs, over which the silk was tightly stretched. The curvature of the wings,
which is shown in the cross-sectional drawing, had a rise of about one-twelfth
the width, the highest point of curvature occurring about one-fourth the dis-
tance from front to rear. Each wing was 64 em. x192 em. (25.25 in. x 75.75 in.),
the two with the tail, in surface equal to a single wing, having an area of 3.7
square metres (40 sq. ft.). The combined weight of the wings was 1150 grammes
(2.53 pounds), and of the tail, 583 grammes (1.28 pounds).

The evolution of a vertical rudder had meanwhile been going steadily for-
ward. Those first used had been small, rectangular, stiff, and heavy, but in the
experiments of May 8 a much lighter and larger construction, consisting of a
frame 92 em.X76 em. (36 in. x30 in.) covered with paper, was used, and on June
7 this was replaced by a long, diamond-shaped rudder, having a spruce frame
covered with silk, very light and seemingly more effective than any hitherto
used.

IT had in the meantime designed a ‘‘ tail-rudder,’’ consisting of a horizontal
tail and vertical rudder combined, each having an area of about 0.6 square
metres (6.5 sq. ft.) which, however, was not used until 1896.

In August was begun the construction of a deeply curved and arched pair
of wings for No. 4, which consisted of a light framing of spruce elaborately
guyed and covered with gold-beater’s skin drawn tight as a drum-head with
pyroxelene varnish. In their construction a new feature, foreshadowed in the
method of guying the separate wings used in the field-trials of May and June,

yas introduced, which was adopted in all subsequent constructions—the guy-
stick, previously described as stretching lengthwise across the wing being now
made a part of the wing itself, which was thus provided with two longitudinal
ribs instead of one. The additional rib occupied a central position, and like
the front rib was attached to the midrod by means of a strong wing clamp.
Its outer end was united to the front rib, which was here bent into a quadrant
of a circle. This pair of wings had an expanse of 435 em. (14.3 feet), an area
of 2.5 square metres (26.8 sq. ft.), a weight of 660 grammes (1.45 pounds), and
a depth of curvature equal to one-tenth their width.

This construction offered a two-fold advantage in its resistance to both tor-
sion and bagging, for as the pressures upon the wing were nearly balanced
about the middle rib, the tendency to twist was reduced to a minimum, while

the bagging, which results from the bending of the framework, as distinct from

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 87

its twisting, was greatly reduced by the manner in which the frame was put
together, the whole construction permitting a return to the system of wire guy-
ing at first adopted, which had been found inapplicable to a wing having but a
single longitudinal rib forming its front margin. When completed, the wings
were strongly guyed with piano wire, both above and below, to guy-posts at-
tached to the midrod, and each cross-rib was separately guyed with wire chords.
Although these wings had cost much in time and labor, and contained many
points of improvement, they were eventually found to be too weak to support
the aerodrome, and were therefore abandoned without a trial in the field.

For the plane horizontal tail hitherto used a pair of curved wings was sub-
stituted, similar in all respects to those just described, but having only half
their area, and these were later replaced by a pair equal in size and in every
way the counterpart of the front wings. The tail as hitherto used accordingly
disappeared, and gave place to another having a wholly different function to
perform; for while the old tail, like the rear pair of wings which superseded
it, was intended to bear a definite part of the weight of the aerodrome, the new
tail which was now added behind the rear pair of wings was not supposed to
bear any part whatever of the weight, but to act solely as a guide, and this new
feature, first introduced in October, 1895, was continued to the end.

This arrangement of the surfaces is quite different from that adopted by
Pénaud in 1872, in which the tail became automatic in its action through its
small angle of elevation as compared with that of the wings, while still acting
as a supporting surface, whereas in the present arrangement the function of
the tail was solely one of guidance. This, I believe, was one of the important
changes which perhaps as much as any other led to final success.

During the fall of 1895 a large number of experiments were made both in
free flight with gliding models, and in constrained flight with the whirling-table,
to determine the relative lifting power of the front and rear wings per unit of
area, and from these the following new rules were deduced for finding the cen-
ter of pressure:

If a following wing is the size of the leader, assume that its efficiency is 66
per cent per unit of surface.

Tf it is half the size of the leader, assume that its efficiency is 50 per cent
per unit of surface.

If it is half as large again as the leader, assume that its efficiency is 80 per
cent per unit of surface.

For intermediate sizes of surface, proportionate values per unit of surface
may be assumed.

If we consider the area of the front wing to be unity, and that of the rear

wing to be n, and if m be the efficiency of the rear wing per unit of surface,

88 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

the above is expressed in the following formule, which it will be remembered

take account only of wings following each other in the same or nearly the same

plane, and are not applicable where one wing is either above or below the plane

of the other. In the formule, CP is the resultant center of pressure upon both

wings expressed in the notation described in Chapter H, CPrw is the center of

pressure of the front wings, and CPrw the center of pressure of the rear wings.
If the value of n lie between one-half and unity,

n+1
m= aj

.

while if the value of x lie between unity and 13,

rm) F4n
15
In either case
CPiwt+mnCP ra
CPp=~-— - s
1l+mn

where the leading and following wings are equal

3CPiw se 2 Ola
5

n=1,m=% and CP=

The steady flight of one of the gliding models referred to led to the con-
struction of a new set of wings for No. 5, patterned after those used on the glid-
ing model. These wings, shown in Plate 17, were rectangular in outline, 200
em. x80 em. (6.56 ft.x 2.62 ft.), each wing having an area of 1.6 square metres
(17.1 sq. ft.) They were constructed with spruce framing covered with China
silk, and were strongly guyed with piano wire in much the same manner as the
light, skin-covered wings already described, which had preceded them. The com-
bined weight of the two pair was 1950 grammes (4.3 pounds).

The long central rib was now much the larger of the two which, as in the
preceding wing, formed the foundation of the structure. It occupied a position
two-fifths the distance from front to rear, and presumably coincided at all points
with the center of pressure of fore and aft sections of the wings, so that the pres-
sure in front of the rib was at all points balanced by the pressure in the rear,
and there was consequently little tendency in the wing to twist under pressure
of the wind. The two main ribs were rigidly connected by cross-ribs of spruce,
20 em. (8 inches) apart, steamed and bent to the desired form. The curvature
of these ribs was the same for all, and in depth was one-twelfth the width of the
wing, while the highest point of curvature was one-sixth of the distance from
front to rear, these ratios having been chosen as approximating those found in
the wing of the soaring bird. These wings were subsequently used in the first

successful flights of the following year.

«

;
.
l

a

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 17

)

)

AN
)

Av
ff

SCALE:
0 20 40 60 80 100 120 140 160C.M.
Guuiiit I jE | J

SCALE:

2 3 4 5 6G 7 8 9 10 C.M,.
tl 1 ai iS SS a ee ee er)

AERODROME NO. 5. PLAN OF WINGS AND SYSTEM OF GUYING

ON

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 89

During the year 1895 but two field-trials were made with the steam aero-
dromes, and neither of these was successful; but a great step forward had been
taken in the construction, guying and arrangement of the sustaining surfaces.
The wings had been made stronger with no increase in weight per unit of area.
On the contrary, the ratio of weight of sustaining surfaces to area had been act-
ually reduced from 45 to 28 grammes per square foot, so that the surfaces were
both lighter and stronger.

Two longitudinal ribs had taken the place of the single one before used, a
second wing clamp had been added to correspond to the midrib, the difficult
problem of torsion had been effectually solved, the system of guying greatly im-
proved, and it appeared that in the next trial the wings might be expected to
bear the weight of the aerodrome without serious distortion.

1896

In January, 1896, two new pairs of wings were designed for No. 6, and in or-
der to give a greater efficiency to the rear wings, they were made larger than
the front ones, the area of the latter being 22 square feet, and of the former 27
square feet, and whereas the width of each wing had formerly been one-third
of its length, it was now increased to two-fifths to correspond to those of No. 5.

The progress made in construction and guying is shown by the facet that
when on January 28 one pair of the wings of No. 5 was inverted and sanded, the
yielding at the tip was less than 5° greater than at the root, whereas at one time
it had been 65°. A similar test applied to a pair of wings of No. 6 on March 4
gave even better results, as the yield at the root was but 1° 45’, and at the tip
2° 30’.

The successive stages of the development of the wing clamps are shown in
Fig. 16. In its final form the front wing clamp, or that which held the main
front rib, shown at AB (1896), had adjustable sliding pieces, by means of which
the wings could be set at any desired angle of elevation, the wing as a whole re-
volving about the rear wing clamp, shown at CD (1896).

The general system of guying the wings, as shown in Plate 17, had been
greatly improved. In the present form a bowsprit and guy-posts firmly at-
tached to the midrod furnished points of attachment for the piano wires with
which the wings were guyed and held rigidly in place, other wires being stretched
across from wing to wing so as to maintain them at a constant diedral angle of
about 150°. The clamps by which the guy-posts were attached to the midrod, are
shown at EF (Fig. 16).

In the successful flights of No. 5 on May 6, the completed wings already de-
scribed weighed together 1950 grammes (4.29 pounds), and had a total sustain-
ing area of 6.4 square metres (68.8 square feet), the flying weight of the aero-

90 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27
drome was 11,775 grammes (26 pounds), and the sustaining surfaces therefore
amounted to 2.6 square feet to the pound, which, as the event proved, was amply
sufficient.

The ‘ tail-rudder,’’? shown in Plate 17, comprised a vertical and horizontal
surface of silk intersecting in a central rod or axis, having a length of 115 em.
(3.8 feet). The framing was of spruce and consisted of two sets of four arms,
each radiating from the central rod, the hexagonal outline of the surfaces be-
ing formed of piano wire, over which the silk was drawn and sewed. The area
of each surface was about 0.6 square metres (6.45 square feet), and the total
weight was 371 grammes (0.8 pounds).

A flat steel spring inserted in the forward end between the rudder and the
midrod gave it a certain desirable degree of elasticity in a vertical direction.
The rudder was held in place by a pin passing through the midrod, and was so
set as to coincide with the line of direct flight, its purpose, as already explained,
being to guide the aerodrome, but to take no part in its sustention.

In balancing Aerodrome No. 5 on May 6, the wings were so adjusted that in

accordance with the notation given above, p. 15:

Ge fu ED
CP n= 141 Dro)

and as the wings were of equal size, from what has preceded in the present

CP Oe 0
5

The center of gravity was located at 1497, so that there should have been a very
slight tendency on the part of the aerodrome to rise, as was actually the case.
The formula was perhaps not quite so accurate as the prolonged flight of the
aerodrome would seem to indicate, as it takes no account of the thrust of the
propellers, which in action tended to elevate the aerodrome in front while their
resistance would tend to depress it when they had ceased to revolve, which con-
sideration accounts for the action of the aerodrome on May 6, as described in
Chapter IX. The formula may, however, be regarded as approximately correct.

In the final successful trial with No. 6 on November 28, 1896, the wings used
were similar in general construction and manner of guying to those of No. 5 on
May 6, but, as shown in the photograph (Plate 29A, Chapter X), the front rib at
its outer extremity was bent to a quadrant to connect with the midrib, this con-
struction being somewhat stronger than that adopted in the wings of No. 5. The
curvature was but one-eighteenth of the width of the wing instead of one-twelfth
as in No. 5. The front and rear pairs were similar and equal and had a com-
bined area of 5 square metres (54 sq. ft.), and a weight of 2154 grammes (4.74

.

~

Sey of

ows

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 91

Ibs.). The flying weight of the aerodrome was 12,120 grammes (26.7 Ibs.), the
sustaining surface thus amounting to slightly more than 2 square feet to the
pound.
The position of the wings, in accordance with the notation adopted, was
CP 0=1563:2,
CP rw=1374.
Since the wings were equal in size,

SS 30 Pig 20 Pee
Opa 2USt Cagis,

The center of gravity was located at 1484, which was 3.5 em. in the rear of the
center of pressure. The flight was approximately horizontal, and the setting
seems to have been as accurate as could be desired. The angle of elevation of
the wings at the root was 10° 30’, and so well were they guyed that there was no
visible yielding at any point during the flight. As the midrod during flight was
approximately horizontal the angle of elevation of the wings may be taken as
10° 30’; the efficiency of the rear wings was two-thirds that of the front wings,
and the effective area was therefore 27+27x3=45 square feet.

The wings being very nearly plane we have therefore the data for deter-
mining the soaring speed from the formula of ‘* Aerodynamies ’’ (Chapter Wale
p- 60).

W=P, cos a=kAV°F (a) cos a,
in which W=26.7 pounds; A=45 sq. ft.; k=0.00166; 2=10° 30’; F (a) cos a=
0.353. By substituting these values in the formula we obtain V=32 feet per
second,

The speed actually attained, however, was about 30 miles an hour, or 44
feet per second, which seems to indicate that the angle of elevation under pres-
sure was reduced to much less than 10° 30’. For a velocity of 44 feet per second,
the theoretical value of « would be but 6°. In this calculation, however, the hull
resistance and that of the system of guy-wires, which must have been compara-
tively large, has been omitted. It would appear, therefore, that the actual re-
sults obtainable in flight are much more favorable than calculations based on

experimental data would presuppose.

CHAPTER IX

HISTORY OF LAUNCHING APPARATUS AND FIELD-TRIALS OF
AERODROMES 4, 5 AND 6

LauNCHING APPARATUS

I have elsewhere mentioned that the difficulties of launching even a very
small model aerodrome are considerable. Early experiments were tried with
an apparatus something like a gigantic cross-bow, and in later years with vari-
ous forms of pendulum, all of which latter brought out the inherent theoretical
defect of the movement of rotation of the aerodrome, and were otherwise prac-
tically inefficient.

A device, consisting of two pendulums, one behind the other, connected by a
rigid rod, from which the aerodrome could be suspended and cast off without ro-
tation, was at one time considered, but abandoned. Experiments were also made
with several forms of railroad, upon which the aerodrome was to run up to the
moment of release, before the form of launching apparatus, which finally proved
successful, was adopted.

All these had failed chiefly for two reasons; first, it was difficult to cause
the aerodrome to be released just at the moment it attained sufficient speed to
soar; second, the extensive surface presented to the wind by the wings of the
aerodrome, made it necessary to provide means for holding the machine se-
curely at several points up to the moment of release without danger of inter-
fering in any way with the aerodrome when it was cast into the air. This proved
a serious problem, which can be appreciated only by one who has seen such a
machine in the open air, where its wings are subject to movement and distor-
tion by the slightest breeze. The steps by which these difficulties were removed
and the final type of launching apparatus perfected are recorded in the following
pages in connection with the field-trials of the model aerodromes.

1892

As the end of the year 1892 approached and with it the completion of an
aerodrome of large size which had to be started upon its flight in some way,
the method and place of launching it pressed for decision. One thing at least
seemed clear. In the present stage of experiment, it was desirable that the aero-
drome should—if it must fall—fall into water where it would suffer little in-
jury and be readily recovered, rather than anywhere on land, where it would
almost certainly be badly damaged.

92

| Ap i ap lite,» dy) tie, Aree tee a eb el

Was «

PED ety sen es ho

=o

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 93

The shores of the Potomac on both banks were scrutinized for this pur-
pose, from a point about two miles above Washington to below Chopawamsic
Island, some thirty miles below the city. Several lofty and secluded positions
were found, but in all these there was the danger that the aerodrome might be
wrecked before reaching the water, or, turning in its course, fly inland; but more
than this, it could be launched only on the rare occasions when the exact wind
was blowing which the local conditions demanded.

Finally, the idea, which seems obvious enough when stated, presented it-
self of building a kind of house-boat, not to get up initial motion by the boat’s
own velocity, but to furnish an elevated platform, which could be placed in the
midst of a considerable expanse of water, if desired, under conditions which
admitted of turning in the direction of the wind, as it need hardly be repeated
that it was indispensable to the machine, as it is to the bird, to rise in the face
of a wind, if there be any wind at all.

The house-boat in question was nothing more than a scow about 30 feet long
by 12 feet wide, upon which a small house was erected, to be used for the occa-
sional storing of the aerodromes. On account of the accidents which were cer-
tain to oceur in the first attempts, it was fitted up with the means of making
small repairs. On the roof of the house there was a platform upon which the
operator stood when making a launch, and upon which were mounted the launch-
ing devices hereafter described.

This boat, shown in Plate 18, was completed in November, 1892.

1893

By the kindness of the Superintendent of the Coast Survey, the house-boat
was towed in May, 1893, down to Chopawamsic Island, a small island near the
western bank of the Potomac River, not far from the Quantico station of the
Washington and Richmond Railroad Company. A map of the island and the ad-
jacent land and water is shown in Plate 19.

The house-boat was at all times moored somewhere on the west side of the
island, in the stretch of quiet water between that and the west shore of the river.
The waters shown here are, with the exception of a narrow channel, very shallow,
and, indeed, partly dry at low tide, so that there was no danger of an aerodrome
being lost, unless its flight carried it a long distance away and over the land.

Fretp Trias *

Aerodrome No. 4, as shown in Plate 11, had a single midrod, a flying weight
of 9 pounds,’ and supporting surface, consisting of wings and tail, of 18 square

1The site of these experiments, which was 30 miles below Washington, has been described.
The writer is designated by the initial “LL”; Dr. Barus, who several times assisted, by the letter
“B”: Mr. Reed, carpenter, by “R”; Mr. Maltby, machinist, by “M”; and Mr. Gaertner, instru-
ment maker, by “G.”

? Weights and dimensions are here given in approximate pounds and feet,

94 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

feet. Its engines, with about 100 pounds pressure, developed an aggregate of
0.4 H. P., and lifted 50 per cent of the flying weight. The propellers were 60 em.
(2 feet) in diameter and 1} pitch ratio.

The aerodrome was intended to be launched by a contrivance called the
‘“ starter,’’ which was an inclined rod, hinged at the bottom, on the top of which
the aerodrome was supported on a rod which was thrown down at the instant
of flight, giving the aerodrome a slight forward impulse, with the expectation
that it would get up sufficient initial speed to soar from the action of its
propellers.

On November 18 the writer (L), with Dr. Barus (B) and the two mechanics
(R and M), went to Quantico by an early train, and superintended with inter-
ested expectation the arrangements for this first trial in the open air of the mech-
anism which had now been over two years in preparation.

We met with an unexpected difficulty—that of launching the aerodrome at
all, for though the wind was only a very gentle breeze, it was only by holding
it down with the hands that it was possible to keep the aerodrome in position
for the launch, during the few minutes which passed from the time it was placed
upon the apparatus to the time of releasing it. Whether the launching device
itself might be effective or not could not be ascertained, since it was found that
nothing which could even be called an attempt to launch could be made except
in an absolute calm; a condition of things very difficult for any one to under-
stand who has not passed through the experience. The writer returned to Wash-
ington at the close of the day without having done anything, but having learned
a great deal.

November 20. L, with B and M, came down again, and waited until 4.20,
when, the breeze having fallen to almost a calm, the aerodrome was maintained
in place on the launching apparatus with great difficulty, while it was repeat-
edly set on fire by the scattering liquid fuel. Finally it was let go, and fell close
to the house-boat, the tail striking the edge of the platform. The immediate
cause of failure was the defective launching apparatus, for the design of which
the writer felt himself responsible.

November 24. L, with B, M, and R came down again to Quantico, but the
very moderate wind proved completely prohibitory to any attempt at launching,
and all returned again to Washington.

November 27. L, with B and M, came down to try a new launching appa-
ratus, not different in principle from the preceding one, but of better construc-
tion. The morning was exceptionally calm, but the engines were found to be
out of order, and precious time was spent in slight repairs which should have
been made in the shop. At 3.30 p. m., when the engines were at last ready, the
exceptional calm gave place to a very gentle and almost imperceptible breeze,

|
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;
;

a ee TL a

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 95

which, nevertheless, again proved prohibitory to the launching, and with ex-
treme disappointment the party returned to Washington, it being at last fully
recognized that unless some way were found of holding down all the extended
supporting surfaces upon the launching piece, and at the same time of firmly
clamping the body of the aerodrome until it could be dropped, as well as of re-
leasing all this simultaneously at the critical instant, no attempt at launching
vas likely to succeed except in such an entire and perfect calm as rarely occurs.
Independent of this launching difficulty, some way of protecting the fires from
the wind had to be found, which was by no means easy, since an efficient pro-
tection meant an enclosure of them and a diminished influx of air, of which it
was essential that there should be an unlimited supply.

December 1. L, with B, R, and M proceeded to Quantico. The same con-
ditions presented themselves and the party returned, without effecting anything.

December 7. LL, B, R, and M present; day overcast but perfectly calm.
Taught by experience, we had everything ready, and a little after one o’clock the
launch was made. The aerodrome fell directly into the boat, the rod of the
starter having broken. It was little damaged, but in view of the injury and
the rising wind, all other attempts were abandoned for the day.

December 11. Present, L, with B, R, and M. A new “ starter ’’ had been
devised and brought down, but was not yet quite ready for use, and an attempt
was made to employ the old one with the improvements suggested by experi-
ence, but, after two attempts to launch, the work was abandoned for the day, ow-
ing this time not to the launching apparatus, but to troubles in the engines and
pumps, due probably to injuries received in the fall of the 7th, which were not
detected until the time of the actual trial.

December 20. L, with B, M, and G, present; engine and aerodrome in or-
der and everything apparently favorable. What seemed to be an almost entire
calm came toward evening, yet once more the all but imperceptible breeze which
prevailed was found to defeat all arrangements for holding the aerodrome to
the launching ways before it was let go.

Trips to Quantico were also made on November 24, and December 1 and 21,
of which no account is given as the very moderate wind which prevailed in each
case precluded any attempt at launching the aerodrome.

It will be seen that eight trips were made to Quantico, and that, far from
any flight having been made, not once even was the aerodrome launched at all.
The principal cause for this lay in the unrecognized amount of difficulty intro-
duced by the very smallest wind, irrespective of the unfitness of the launching
apparatus to give the desired initial speed and direction.

In all these trials, the aerodrome rested on the launching apparatus, by
which it was projected forward by means of a spring in such a way as not to
interfere with the propellers.

-
96 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. Di

Previous tests with the rubber-driven models had demonstrated the futility
of all simple pendulum types of ‘‘ cast off,’’? and likewise all the trials hitherto
of a railroad form of launching apparatus, in which the aerodrome was mounted
on a car, which had itself to get out of the way, were equally failures, so that
when the device referred to above proved to be worthless, it seemed that almost
every plan had been exhausted. There were, moreover, other difficulties, some
of which have been indicated above, such as that of making the burners work
properly in even a moderate wind during the very short time required for at-
taching the wings and so adjusting the aerodrome on the launching apparatus.

These difficulties, which, now that they have been overcome, seem difficul-
ties no longer, but which then seemed insuperable, were all connected with the
ever-present problem of weight. It would have been easy to make rigid sustain-
ine surfaces which would not bend ii the wind; to make fires which would not go
out; and easy to overcome all the impediments which seem so trivial in descrip-
tion and were so formidable in practice, were it not that the mandate of abso-
lute necessity forbade this being done by any contrivance which would add to
the weight of an already phenomenally light construction. The difficulties of the
flight as they were seen in the workshop were multiplied, then, beyond measure
by the actual experiments in the field, and the year closed with a most discour-
aging outlook.

1894

The new year began without any essential improvement in the means al-
ready described, though a new launching apparatus had been devised by the
writer, which was scarcely so much an apparatus for launching, in the ordinary
sense of the word, as one for holding the aerodrome out over the water, and
simply letting it drop from a height of about 25 feet, during which fall it was
hoped (exact data being unobtainable in advance of experiment) that there
would be time for the propellers to give the aerodrome the necessary soaring
speed before reaching the water. This device consisted of an inverted tripod,
which held the aerodrome comparatively steady by three bearing points, while
a cross-bar of wood was added to prevent the wings from swaying before the
launch. Previously, the supporting surfaces, wings and tail, had been put on
only at the last minute. Now it became possible to keep them on in a gentle
breeze for an indefinite time before launching.

January 9. The previous day having been spent in practicing the steps pre-
liminary to launching, so as to avoid delay in assembling and mounting the aero-
drome, the writer, with Dr. Graham Bell, went to Quantico. The day was calm,
and every condition seemed favorable. The aerodrome was dropped fairly, un-
der full steam, and it fell in a nearly horizontal position, but touched the water
at a distance of only 50 or 60 feet, evidently before the necessary initial speed

-

a

an

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 97

could be impressed on it by its engines. The conclusion should have been that
by this method nothing but a practically unsuitable height would suffice to start
the aerodrome in a calm, though it might perhaps be done in the face of a con-
siderable breeze.

May 25. After a considerable interval of delay, due to the river being closed
by ice and other causes, Aerodrome No. 4 was again dropped from the starter
under nearly the same conditions as in the trial of January 9, and with a quite
similar result, the final conclusion being that this method must be abandoned.
It may be added that a vertical rudder was tried on this day.

June 12. No. 4, with an improved blast, was tried at Quantico, Mr. Goode
being present. The day ended in failure from another cause, the improved
blast, which worked well in the shelter of the shop, but proved useless in the field,
being extinguished by the feeblest wind. At this time (in June and July) I de-
signed a horizontal railroad with launching springs and track, underneath which
ran a car which held the aerodrome firmly until the moment of automatic release.
This apparatus finally proved to be the successful solution of the launching
problem. The description given later, with the drawing in Plate 18, shows the
after-improvements, but no specific change from that in use from the first.

About this time I also arranged for certain changes in the boilers and
burners, having decided that I would not go into the field without some ground
for confidence not only that the aerodrome could be Jaunched successfully, but
that a steady flame could be maintained under the boilers.

October 6. No. 4, as remodelled, having a flying weight of about 14.5 pounds,
a supporting surface of about 28 square feet, with a total engine power of about
0.5 H. P., and having lifted 40 per cent of its weight on the pendulum, was taken
down the river for trial with the new railroad launching apparatus, and several
days were spent in erecting the launching apparatus on the house-boat, and in
launching ‘‘ dummy ’’ aerodromes from it for practice.

Aerodrome No. 4 then being fitted under conditions which apparently in-
sured a good start (the center of pressure being nearly over the center of gray-
ity, the root angle of the wing being zero, the midrod nearly horizontal, the
engine working well, and with apparently ample sustaining surface) was finally
successfully launched, but the hopes which were reasonably entertaied proved
to be unfounded. The result of this first actual trial of a ‘‘ flymg machine ”’ in
free air was most disconcerting, for the aerodrome, which had in theory many
times the power required for horizontal flight, plunged into the water with its
engines working at full speed, after a course hardly longer than that performed
by the dummy. This result was at first inexplicable.

No. 4, then, did not fly at all, from some at first inscrutable cause, and it was

decided to make a trial of No. 5, though it was hard to put the result of so much
8

98 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

time, painstaking and cost to the hazard of destruction. With the experience
just acquired from the trial of No. 4, the wing of No. 5 was set at an angle of
about 20° with the midrod, and the tip was secured by a light cross-piece, so
guyed that the wing as a whole, while set at this considerably greater angle with
the rod, was stiffer than before. In addition to this, the air chamber was moved
back so that the center of gravity was from 6 to 10 em. behind the (caleulated)
center of pressure. These changes were made in order to insure that the front
should at any rate keep up, and it did.

The aerodrome was launched successfully with the engines working under
a pressure of 110 pounds of steam. The head rose continually until the mid-
rod stood up at an angle of about 60°, checking all further advance. It re-
mained in the air ina stationary position for nearly a second, and then slid back-
ward into the water, striking on the end of the rudder and bending it. The dis-
tance flown was about 12 metres, and the time of flight 38 seconds. One of the
propellers was broken short off, and the shaft was bent.

It thus became clearly evident that some cause prevented the proper balan-
cing of the machine, which was necessary to secure even approximately the the-
oretically simple condition of horizontal flight. It was all-important that the
angle of the front wing should be correct, but its position could not be accurately
known in advance of experiment, and this experiment could only be made with
the machine itself, and involved the risk of wrecking it.

These trials gave a very vivid object lesson of what had already been antici-
pated,’ that the difficulties of actual flight would probably le even more in ob-
taining exact balance than in the first and more obvious difficulty of obtaining
the mere engine power to sustain a machine in the air. The immediate problem
was to account for the totally different behavior of the two aerodromes in the
two flights, under not very different conditions.

Observations of the movement of the two aerodromes through the air, as
seen by the writer from the shore, seemed to show, however, that the wings
did not remain in their original form, but that at the moment of launching there
was a sudden flexure and distortion due to the upward pressure of the air. The
time of flight was too short, and the speed too great, to be sure of just what did
occur, but it seemed probable that the wings flexed under the initial pressure of
the weight which came upon them at the moment of launching, and that they
were in fact, while in the air, a wholly different thing from what they were an
instant before, so that a very slight initial difference in the angle at which they
first met the air might cause the air to strike in the one case on the top of the
wings and throw the head down, and in the other ease so as to throw the head up.
To ascertain the extent and character of this flexure, caused, it will be observed, by

®’“ Pxperiments in Aerodynamics.”

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 99

the weight of the aerodrome suddenly thrown on the wings, I inverted the aero-
drome and distributed a weight of dry sand equal to that of the whole machine
evenly over the supporting surfaces. It was found that under the weight of the
sand the extremity of the wings bent to an angle of 45° downwards (and con-
sequently must have bent to an angle of 45° upwards in the air), a condition of
affairs worse than anything that had been suspected, and seeming to demand
the entire reconstruction of the wings with a strength and consequent weight
for which there was no means of providing.

There had been some injuries to the machines in the trials of the 5th and
6th, and these were repaired. A new float had been made for No. 4, and a new
set of larger wings for No. 5. Hach of these wings had a length of 76 inches
and a breadth of 25 inches, making the total surface of the two 26.4 sq. ft., while
that of the tail was 13.2 sq. ft., or about 40 sq. ft. in all.

October 22. When No. 5 was finally prepared for another trial, its condi-
tion was as follows:

AMeyA TS ecwy CLE barcyevcy coals ois) ayerNiarsvavsicranciave nce mia oicediGieve aves 22 pounds

Area of supporting surfaces (wings and tail)..... 40 sq. ft.

Sq. ft. of surface per pound of weight............ 1.84

Engine power with 115 lbs. steam pressure........ OBE be

Power MeCessary: tO SOal tina. scicicletetets xsoteenraiew ee Osburn e

Theoretical soaring speed (plane wings at 20°).... 24 ft. per sec.

EreviOusmitt sOnnp CWO WHEN. coc. jonevarerereskiass eis. save) e-ars 40 per cent of flying weight

October 25. The aerodromes having been taken to Quantico on October 23,
and satisfactory experiments made with dummies in order to test the launching
apparatus, the house-boat was carried out into midstream and moored.

Aerodrome No. 4 was launched in the face of a wind of about 1100 feet per
minute. The midrod was at a very small inclination with the horizontal, about
3°. The angle (a) of the chord of the curved wing measured at the rod, where
it was rigidly held, was 15°. The adjustment was such as to bring the CG im-
mediately under the CP, without any allowance for the fact that the line of pro-
peller thrust was below the CP.°. The aerodrome under these conditions was
launched with the head high. It made a real, though brief, flight of about 130
feet in 44 seconds, when it swung abruptly round through 90°, and, losing head-
way, sank continuously, finally falling backward into the water.

October 27. Aerodrome No. 4, having been repaired and guyed with wires
from the wings to vertical guy-posts beneath, was launched again, but one of the

*On the data of “ Aerodynamics,” a plane having 1.8 sq. ft. of surface per pound, and advancing
at an angle of 20°, would soar at a speed of 24.1 ft. per second.

*It will be remembered that the purely theoretical conclusions just cited apply to the power
delivered in direct thrust, but that of the above actual H. P. an indefinite amount was lost in friction
and slip of propellers.

*It may be observed that at this time the position of the CP was calculated on the assumption
that the pressure for flight surfaces was proportional to the areas, without also allowing for the
fact that the following surfaces, like the tail, were under the “lee” of the wind and so far less
efficient. It follows, then, that the value CP — CG was not really 0, as was assumed, but something
considerable.

100 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vot. 27

guy-wires caught on the launching car, and threw the aerodrome immediately
into the water with but little damage.

On the same day No. 5 was launched. The theoretical CP—CG was nomi-
nally 0, but, for the reasons stated in the footnote on p. 99, was really something
positive, that is to say, the CP was really somewhat in advance of the CG; in-
clination of midrod less than « (=20°). The aerodrome under these cireum-
stances, while keeping its head up, at first fell rapidly, yet seemed about to rise
just as it struck the water, conveying the idea that if the launching had been
made with a greater initial velocity it would have risen and cleared the water.
The wings visibly pocketed, however, and it was clear that some better dispo-
sition must still be made for them. The flight was 34 seconds.

No. 5 was tried again on the same day with larger wings, whose area was 40
square feet. These wings, though stiffer, pocketed a little. «=20° as before. It
flew rapidly, and at first horizontally, to a distance of 100 feet or more against
a five-mile breeze. It then turned abruptly round through 180°, at first falling
(from loss of headway), then distinctly rising, and at the same time throwing
its head up until it reached an angle of nearly 60° with the vertical, when it fell
backward after a flight of between 6 and 7 seconds. The wings were evidently
not yet strong enough to resist flexure.

November 21. No. 5, in nearly the same condition as before. Two extra
springs had been placed on the launching car, in order to give the aerodrome a
greater initial velocity than before. Everything appeared favorable, but as it
left the launching track a piece flew out of the port propeller, in spite of which
the aerodrome, after dropping 5 feet, rose bodily at an angle of 45° and fell
backward into the water (time, 5 seconds).

Another trial was made the same day with the same aerodrome, under sim-
ilar conditions, except that the angle of inclination (a) was reduced to 7°. It
now, with all the other circumstances of launching like those immediately be-
fore, behaved entirely differently, plunging head downward into the water at
a distance of 30 feet. Once more it was shown beyond dispute that the wings
must somehow be made even stiffer.

December 8. Another trial was undertaken with No. 5, the CG being 10 cm.
in front of the CP at rest. The root angle of the wings was 18°, tip angle 27°,
elevation of midrod 1 in 24. The other changes made since the previous trial
consisted chiefly in the increased weight due to the longer and stronger frames
and shafts that were made to carry 100 em. propellers. The flight obtained was
so short that it was as unsatisfactory as before.

The aerodrome rose in the air after leaving the launching apparatus, and
then slid back into the water in the plane of its own wings. On the first trial, it
struck the boat, and was slightly injured; on the second, with root angle of

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 101

wings 10°, tip angle 20°, the flight partook of the same character, but the ma-
chine struck the water clear of the boat.

The fact that with the CG 10 em. in advance of the calculated CP the aero-
drome steadily rose in front, seems to indicate that the rule used at that time for
calculating the CP (see Chapter IL) was not very accurate. This rule was based
upon the assumption that the tail, having an area equal to one-third the entire
sustaining surface, supported one-third the total weight (expressed by the for-

20Pum+ CP. m .
Te Ne eae , Where CPwm and CPim represent respectively the CP

of the wings and tail in motion), and that the CP of each surface was one-fifth
its width in front of the center of figure.

December 12. Four days later, the tail had been moved back 21 em., thus
carrying the CG back 7 em., but the vertical rudder (weighing 105 grammes),
for which there was now no room, was taken off, which in a measure counter-
acted this change.

A trial was then made with the wings set at an initial angle of 8° at the
root and 20° at the tip. The aerodrome was released with the engines working
under a steam pressure of 90 pounds, and soared off horizontally for some dis-
tance, when suddenly it swerved to the right as though something on that side
had given out, and turning quite through 180° headed toward the boat, striking
the water about 76 feet away. The time of the flight was 4 seconds.

It was found upon the recovery of the machine that one of the propellers
had been twisted through 90°, so that the two were no longer symmetrical. The
turning may have been due to this twist or to unequal influence of the wind
upon the two wings; for when I applied the sand test to the wings after return-
ing them to Washington, it was found that they deflected so much that the grains
would not lie upon them, which, to a great extent, explains the failure to secure
a better flight.

Thus the end of another year had been reached, and what might be called a
real flight had not yet been secured. The only progress that seemed to have been
made was that the aerodromes were not quite so unmanageable and erratic in
their flights as at the beginning of the year, and that it had been demonstrated,
at least to the writer’s satisfaction, that the power was sufficient for the work to
be done. The launching device had been so perfected that it worked satisfac-
torily, but the problem of balancing seemed as far from solution as before.

1895

While, for convenience in narrating the progress of the work with the aero-
dromes, each year has been treated as a unit, it is, of course, understood that
the work itself shows no especial difference between the closing of one year and
the beginning of another. Changes which had important effects were introduced

fod

102 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

at various times, but were, of course, made as they suggested themselves with-
out any reference to time or season. But while it was customary to make, from
time to time, a résumé of the progress of the work, yet at the closing of the cal-
endar year it was the custom to make a more complete digest of just what had
been accomplished during the year.

Upon thus reviewing the progress of the work during 1894, it was felt that
the results which had been accomplished for such a large expenditure of time
seemed small, since no real flight had been made by any of the aerodromes, and
no definite assurance that a successful flight would be obtained within the imme-
diate future seemed warranted by what had already been accomplished. But
now that the principal difficulties connected with the launching apparatus had
been overcome, thus permitting the aerodromes themselves to be given a fair
trial, the belief was encouraged that the continuance of the actual tests of the
machines, with slight changes which previous tests had shown advisable, would
finally result in a successful flight.

The early weeks of 1895 were spent in a series of pendulum tests on No. 5,
and in making such slight changes as these tests indicated would be advisable.
As a result of small improvements introduced in the boilers, No. 5 had by the
middle of March shown a repeated lift of considerably over 50 per cent, and in
some tests as much as 62 per cent of its flying weight. Certain radical changes
previously deseribed in Chapter VII were also made in Aerodrome No. 4, and
in the pendulum tests of it a lift of 44 per cent of its flymg weight had been
obtained. :

Encouraged by the better results which the aerodromes had shown in the
above tests, it was decided to test them again in free flight, and they were ac-
cordingly sent down to Quantico in charge of the two mechanics, R and M, Mr.
Langley, accompanied by Dr. Graham Bell, whom he had invited to witness the
tests, following on May 8. On the evening of May 8 No. 5 was mounted on the
launching apparatus in order to drill the mechanics so that when favorable
weather presented itself the aerodrome could be got ready for launching with the
minimum delay.

On May 9 Mr. Langley and Dr. Bell reached the house-boat at 5 a. m., but
even with the drill of the previous evening the mechanics were not able to have

No. 5 ready for trial until 6.15 a.m. The principal conditions of No. 5 at this
time were:

Total weight 11,200 grammes (24.6 pounds), including 800 grammes of
fuel and water. Previous lift on the pendulum 54 per cent, with a steam pres-
sure of 150 pounds. With this steam pressure the engine made about 600
R. P.M. when driving the 95 em. propellers, which through their reduction
gearing made about 500 R. P. M.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 103

When the aerodrome was balanced for flight so as to bring the theoretical
‘* center of pressure in motion ’’ over the center of gravity, it was found that it
was not possible to carry the center of gravity in front of this point, although
it was known by experience to be necessary. Accordingly in the first trial the
outer ends of the tail were pressed down by the guys so that the wind of ad-
vance tended to lift the tail and throw the head down more than if the tail had
been flat. Furthermore, the float, weighing 200 grammes, instead of being placed
in its normal position near the base of the bowsprit, was carried out to its ex-
tremity, this change in the position of the float alone being sufficient to carry the
center of gravity forward three or four centimetres. The curved wings were
set at an angle of nine degrees at the root and eleven degrees at the tip. They
were well guyed, and in flight appeared to be not materially twisted or altered.

It was anticipated that the pressing down of the outer ends of the tail and the
shifting of the center of gravity would cause the aerodrome to point downward in
flight, and this anticipation was verified in the test. At 6.15 a.m. the aerodrome
was launched at a steam pressure of 120 pounds. A perfect calm prevailed at
the time and the machine started straight ahead. There was no perceptible
drop at the moment it was released from the launching car, but a smooth and
steady descent until it struck the water, nose down, at a point approximately
200 feet from the boat. Dr. Bell noted that the length of time the aerodrome
was in the air was 2.8 seconds. One of the propellers was broken and the other
one was found to have twisted its shaft one-fourth of a turn.

At 9.45 a.m., the wings having been dried, No. 5 was again tried. The
float was moved back to its normal position at the base of the bowsprit, and the
guys, by which the outer ends of the tail had been depressed in the previous
trial, were so adjusted that the tail was flat. The machine was, therefore, in
the condition of theoretical equilibrium for rapid motion with a plane wing. All
the other conditions were precisely as in the previous trial, except that the
round-end 100-centimetre propellers were substituted for the 95-centimetre ones
which had been broken, and a new paper-covered tail was used. The mechanic
in charge was directed to let the steam reach its highest pressure consistent
with a flight of one-half a minute, before launching the machine, but he seemed
to have lost all sense of the length of time the fuel and water would last, as he
let the engines run until almost the whole charge was exhausted before launch-
ing it. The aerodrome went off almost horizontally, then turned up into the
wind and rose to an angle of about twenty degrees; then (while moving for-
ward) slowly sank as though the engine power had given out, as in fact it doubt-
less had. The actual distance travelled was 123 feet and the length of time 7.2
seconds. While the exhaustion of the fuel and water prior to launching the ma-

chine had prevented what apparently would otherwise have been an exceed-

104 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

ingly good flight, yet the fact that the aerodrome rose immediately after being
launched, and continued to do so until the power gave out, was in itself very
encouraging.

At 140 p. m. No. 5 was again ready for trial (the third one for the day),
and this time Mr. Langley and Dr. Bell witnessed it from a greater distance in
hopes of being able more clearly to study its behavior when actually in the air.

The previous trial having missed suecess through the fuel and water hav-
ing been consumed before the machine was launched, special instructions were
given to avoid the recurrence of this mistake. But the machine was held for
probably two minutes after the burners were lighted, with very much the same
result as before. The conditions of the aerodrome were the same as in the
previous trial, except that the tail was a little flatter, so as to tend to make the
head slightly lower in flight. It was launched at an angle of about thirty de-
grees with the very gentle wind that was blowing, and, apparently under the di-
rection of the rudder, turned into the wind, the midrod rising to an angle of
about twenty degrees and (as noted in Mr. Langley’s record book) ‘‘ The whole
machine absolutely rising during five or six seconds—a fine spectacle! Then
the power visibly gave out, the propellers revolving slower. It settled forward
and lost nearly all of its forward motion at the end of about seven seconds, but
did not finally touch the water until ten and a quarter seconds.’’

While the length of time that the aerodrome had been sustained in the air
was so short that no actual flight had really been achieved, yet the results en-
couraged the belief that with the aerodrome more accurately balanced, it could
reasonably be hoped that a somewhat longer flight would be obtained. It was,
however, very evident that, although the correct balancing which would in-
sure equilibrium for a few minutes might soon be attained, the machine, lack-
ing a human intelligence to control it, must be provided with some mechanism
which would tend to restore the equilibrium, the conditions of which must nee-
essarily change in a machine depending on the air for its support. In order
to see what could be done in this direction, it was, therefore, decided to return
immediately to Washington with the machines and make some minor changes
in them before attempting further flights.

By the end of May, Nos. 4 and 5 were again in readiness for a trial, and
the mechanics were accordingly sent to Quantico to complete preparations for
the tests. During May Mr. A. M. Herring, who had been experimenting with
model machines for several years, was engaged for a few months as an assist-
ant, and he was immediately put in charge of the field trials of Nos. 4 and 5,
which were now about to be made. On June 6 Mr. Langley, accompanied by
Mr. Herring, went to Quantico, and on June 7, at 5 a. m., Aerodrome No. 5 was
ready for trial, but the wind was so high that nothing could be done. The wind
later diminished in intensity, but the house-boat had become stuck on the beach

NiOeates LANGLEY MEMOIR ON MECHANICAL FLIGHT 105

and it was impossible to make the launching apparatus point directly into the
wind, which was blowing from the rear of the boat. An attempt was made to
launch the aerodrome even with the wind blowing at its rear, but it was found
impossible to make the fires burn and the test was accordingly postponed. Later
in the afternoon the house-boat was floated and the preparations for a test were
immediately completed. At 5.42 p. m. the fires were lighted, but the burners did
not work properly and the proper steam pressure could not be obtained. At
6.20 p. m. the fires were again lighted, and at 6.22 the aerodrome was launched,
its midrod having an upward angle of 25 degrees, or more, with the launching
track. The aerodrome moved off nearly horizontally, but seemed to be very
sluggish in its movement and fell in the water about seventy feet from the boat,
after having been in the air only 4.8 seconds. The damage consisted of a broken
propeller and a slight strain in the main frame, the extent of which, however,
was not immediately seen.

The steam pressure at the time of launching was 110 pounds, which was e@b-
viously insufficient. The aerodrome had lifted fifty per cent of its weight on the
pendulum, and its sluggishness of movement seemed, therefore, unaccountable
even for this pressure. It seemed probable, however, that the pressure ran down
immediately after the machine was launched, on account either of the use of
the light-weight burners in place of the larger and heavier ones, or of the dim-
inution of the air pressure in the gas tank.

At 7.55 the aerodrome was again launched, and this time made a still shorter
flight than before, being in the air only three seconds. A serious leak in the en-
gine cylinder was, however, discovered just as the machine was launched, and
this probably accounted for the lack of power.

Not only had the tests which have just been described indicated that there
was a lack of power during flight, although previous pendulum tests had repeat-
edly shown lifts greater than fifty per cent, but, furthermore, the wings them-
selves, while appearing perfectly capable of supporting the aerodrome when
viewed with the machine stationary, were seen to flex to such an extent in flight
that it seemed probable that much of the power was consumed in merely over-
coming the head resistance of a large portion of the wings which had lost all
lifting effect.

During the fall and winter, as recorded in Chapters VII and VIII, Aero-
drome ‘‘ New No. 4,’’ which had been reconstructed during the summer, and
which upon test wes found radically weak, was almost entirely rebuilt and after-
wards known as No. 6. Important changes were also made in No. 5, which
greatly increased its strength and power. The improvements, however, which
contributed more than anything else to the marked suecess achieved in the next
trial of the aerodromes, were those which had to do with the nature and dispo-
sition of the sustaining surfaces and the means for securing equilibrium.

~ i? a

106 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 2.

It will be recalled that in the more recent trials the apparent causes of fail-
ure had been the inability to provide sufficiently rigid wings, the great difficulty
of properly adjusting the relative positions of the centers of pressure and grav-
ity, and the lack of any means of regaining equilibrium when the balance of the
aerodrome had in any way been disturbed. In the fall of 1895, accordingly, it

vas finally decided to employ a second.pair of wings equal in size to the first or

leading pair. This not only added greatly to the stability of the aerodrome, but
also made it possible, without any alteration in the plan of the frame, to bring
the center of pressure into the proper position relative to the center of gravity.
In addition the plan of constructing the wings was modified by the introduc-
tion of a second main rib, which, placed at approximately the center of pres-
sure of the wings, made them much stiffer, both against bending and torsion.
The two pairs of wings now became the sole means of support, and the tail
which had hitherto been made to bear part of the weight of the aerodrome, as
well as assist in preserving the longitudinal equilibrium, was now intended to
perform only the latter function. It was placed in the rear of the wings and
was combined with the vertical rudder. Further, in adjusting it on the aero-
drome, it was set at a small negative angle and given a certain degree of elas-
ticity, as described above. This device proved to be a most efficient means of
maintaining and restoring the equilibrium, when it was disturbed, and its value
was apparent in all future tests of the models.

1896

The important changes in the steam-driven models which had been begun
in the previous fall, and which in the case of No. 4 had been so extensive as to
convert it into a new aerodrome, No. 6, were continued during the early spring,
and it was not until the last of April that the models Nos. 5 and 6 were ready
for actual test in free flight.

The condition of No. 5, which made the first successful flight, is given in
the data sheet for May 6, 1896, and its general form at this time may be seen
in the photograph of May 11, Plate 27A. Although the changes described above,
as well as the modifications in the boilers and burners of both aerodromes had
undoubtedly effected a great improvement in every detail of the machines, the
disappointments experienced in the preceding years prevented any great feeling
of confidence that the trials which were now to be made would be entirely suc-
cessful. On May 4, however, the two mechanics, Mr. Reed and Mr. Maltby, were
sent down to Quantico with Aerodromes Nos. 5 and 6, and Mr. Langley, accom-
panied by Dr. Graham Bell, who had been invited to witness the tests, followed
on the afternoon of the 5th. On May 6 the wind was so very high all the morn-
ing that a test was found impracticable. During the forenoon, however, the
wind gradually died down, and by 1 p.m, was blowing from six to ten miles an

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 18

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 107

hour from the northeast. At 1.10 p.m. Aerodrome No. 6 was launched, but the
guy-wire uniting the wings having apparently caught on one of the fixed wooden
strips which held the wings down, the left wing was broken before the aero-
drome was really launched, and the result was that the machine slowly settled
down in the water by the boat, breaking the propellers and slightly injuring
the Pénaud tail.

After removing No. 6-from the water, No. 5 was placed on the launching
car and immediately prepared for a test. At 3.05 p. m. it was launched at a
steam pressure of 150 pounds and started directly ahead into the gentle breeze
which was then blowing. The height of the launching track above the water
was about twenty feet. Immediately after leaving the launching track, the aero-
drome slowly descended three or four feet, but immediately began to rise, its
midrod pointing upward at an increasing angle until it made about ten degrees
with the horizon and then remained remarkably constant at this angle through
the flight. Shortly after leaving the launching track the aerodrome began to
circle to the right and moved around with great steadiness, traversing a spiral
path, as shown in the diagram (Plate 19). From an inspection of the diagram,
it will be noticed that the aerodrome made two complete turns and started on the
third one. During the first two turns the machine was constantly and steadily
ascending, and at the end of the second turn it had reached a height variously
estimated by the different observers at from 70 to 100 feet. When at this height,
and after the lapse of one minute and twenty seconds, the propellers were seen
to be moving perceptibly slower and the machine began to descend slowly, at
the same time moving forward and changing the angle of inclination of the
midrod until the bow pointed slightly downward. It finally touched ‘the water
to the south of the house-boat at the position shown, the time the machine was
in the air having been one minute and thirty seconds from the moment of launch-
ing. The distance actually traversed, as estimated by plotting its curved path
on the coast-survey chart and then measuring this path, was approximately 3300
feet, which is the mean of three independent estimates. This estimate of the
distance was checked by noting the number of revolutions of the propellers as
recorded by the revolution counter, which was set in motion at the moment the
machine was launched. On the assumption that the slip of the propellers was
not greater than fifty per cent, the 1166 revolutions as shown by the counter
would indicate a distance travelled of 2430 feet. As it was felt very certain
that the slip of the propellers could not have amounted to as much as fifty per
cent, it seemed a conservative estimate to place the length of flight at 3000 feet,
which would mean a rate of travel of between 20 and 25 miles an hour. The cir-
cular path traversed by the aerodrome was accounted for by the fact that the
guy-wires on one of the wings had not been tightened up properly, thus causing
a difference in the lifting effect of the two sides.

108 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

The aerodrome was immediately recovered from the water and prepara-
tions made for a second test, the machine being launched again at 5.10 p. m. at a
steam pressure of 160 pounds. The conditions were the same as at the first trial,
except that the wind had changed from north to south and was perhaps of less
velocity than before. The path traversed by the aerodrome in this second trial
was almost a duplicate of the previous one, except that on account of the change
in the direction of the wind the machine was launched in the opposite direction.
In tightening up the guy-wires, which had not been properly adjusted in the pre-
vious test, they were probably tightened somewhat too much, since in this sec-
ond test the aerodrome circled towards the left, whereas in the first flight it had
circled towards the right. The aerodrome made three complete turns, rising
to a height of approximately sixty feet with its midrod inclined to the horizon
at a slightly greater angle than before. The propellers again ceased turning
while the machine was high in the air and it glided forward and downward and
finally settled on the water after having been in the air one minute and thirty-
one seconds. The distance travelled was estimated as before, by plotting the
path on the coast-survey chart, and was found to be 2300 feet.

During these flights several photographs were secured of the machine while
it was actually in the air, some of the pictures being taken by Dr. Bell and others
by Mr. F. E. Fowle. The clearest of these are shown in Plates 20, 21, and 22.

Just what these flights meant to Mr. Langley can be readily understood,
They meant success! For the first time in the history of the world a device pro-
duced by man had actually flown through the air, and had preserved its equi-
librium without the aid of a guiding human intelligence. Not only had this de;
vice flown, but it had been given a second trial and had again flown and had
demonstrated that the result obtained in the first test was no mere accident.

Shortly after returning to Washington, Mr. Langley left for Europe, but
before doing so he gave instructions to the workmen to remedy the small weak-
nesses and defects which had been found in Aerodrome No. 6, and to have both
aerodromes ready for trial before his return in the fall.

After returning in the fall, Mr. Langley again had Aerodromes Nos. 5 and
6 taken down to Quantico for trial, and this time had as his invited guest Mr.
Frank G. Carpenter. On November 27 a test was made of Aerodrome No. 6,
the general disposition of which at this time may be learned from the description
in Chapter X, and the photographs in Plates 29A, 29B. The model was launched
at 4.25 p.m. with a steam pressure of 125 pounds. The aerodrome went nearly
horizontally against the wind, and descended into the water in six and a quarter
seconds at a distance of perhaps 100 yards. After the machine had been re-
covered from the water, it was found that a pin had broken in the synchronizing
rod which connects the two propeller shafts together, and that the counter, which
showed 495 revolutions of the propellers, had been caused to register inaeccu-

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 21

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MAC RIVER, MAY 6, 1896. ENLARGED TEN TIMES

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 22

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 109

rately on this account. The balancing of Aerodrome No. 6 had been made the
same as that of No. 5, but in No. 6 the line of thrust was twelve centimetres
higher, and this fact, which had not been taken into account in determining the
proper balancing for No. 6, seemed to be sufficient cause for the aerodrome
coming down into the water so soon after being launched. Darkness had de-
scended before the aerodrome could be recovered and prepared for a second
trial. On the next day, November 28, a high wind prevailed in the morning,
but in the afternoon it became comparatively calm, and No. 6 was launched at
4.20 p. m. under the same conditions as on the preceding day, except that the
float, which weighed 275 grammes, was moved back from the bowsprit eighty
centimetres in order to make the machine lighter in front. The aerodrome was
launched at a steam pressure of not much over 100 pounds, the air draft for
the burners being temporarily bad. The midrod made an angle of approximately
three degrees with the horizontal. On account of a slight rain, which had oc-
curred just before the machine was launched, the wings were wet and the weight
of the entire aerodrome was doubtless as much as twelve kilos. Immediately on
being launched the aerodrome started directly ahead in a gentle south wind,
moving horizontally and slowly turning to the right and appearing to approach
dangerously near to some’ thick woods on the west shore. However, it fortu-
nately continued turning until it pointed directly up the beach with the wind
in the rear. It then moved more rapidly forward, dipped and rose but once,
and this very slightly, and continued its remarkable horizontal flight, varying
not more than two yards out of a horizontal course, and this only for a mo-
ment, until it finally descended into the bay at a point nearly in a line between
the house-boat and the railroad station at Quantico. Upon being recovered, it
was found to be absolutely uninjured, and another flight would have been made
with it immediately but darkness had descended. The time of flight, as deter-
mined independently by two stop-watches, was one minute and forty-five see-
onds. The number of revolutions of the propellers was 2801, or at the rate of
1600 R. P. M., which, with an allowance of fifty per cent slip, should have car-
ried the aerodrome a distance of 4600 feet in one and three-quarter minutes.
While the distance from the house-boat in a straight line to the point at which
the aerodrome descended was only about 1600 feet, vet it was estimated by those
present that this straight-line distance was certainly not greater than one-third
the total length of the path traversed, which would mean a distance of something
like 4800 feet. The length of the course, as plotted on the coast-survey map
and afterwards measured, was 4200 feet, and it, therefore, seemed safe to say
that the total distance travelled was about three-quarters of a mile, and the
speed was, therefore, about thirty miles an hour.

10

CHAPTER X

DESCRIPTION OF THE LAUNCHING APPARATUS AND OF AERO-
DROMES Nos. 5 AND 6

Reference has already been made to the development of the ‘‘ cast-off ’’
apparatus that was used at Quantico for launching the aerodrome. An initial
velocity is indispensable, and after long experiment with other forms which
proved failures, an apparatus was designed by me, which gave a sufficient linear
velocity in any direction. It had, moreover, been found that, when the aero-
drome was attached to any apparatus upon the roof of the house-boat, such
slight changes in the direction and intensity of the wind as would ordinarily pass
unperceived, would tend to distort or loosen it from its support, so that only
the most rigid of fastenings at three independent bearing points were of any use
in holding it, while the wings must be separately fastened down, lest they should
be torn from their sockets. It was, then, necessary to be able to fasten the
aerodrome very firmly to the cast-off apparatus, to start it upon its journey in
any direction with an initial linear velocity that shold equal its soaring speed,
and to release it simultaneously at all points at the very same instant, while at
the same time the points of contact of the launching device, to which it had just
been fastened, were themselves drawn up out of the way of the passing pro-
pellers and guys.

All these requirements and others were met by the apparatus finally adopted,
which is shown in Plates 23 and 24. It consists of a strong timber frame-work,
carrying a track, consisting of two flat iron rails set on edge, upon which runs
the launching car, suspended from two small wheels on each side. At the front
end of the frame there are two cylindrical air buffers to receive the buffing pis-
tons and thus stop the car after the aerodrome has been released. The car is
drawn to the rear end of the track and held by the bell-erank lever A (Plate 23).
The contact points BB and C are turned down and the elutch-hook D set over the
elutch-post K. The aerodrome is thus held firmly up against the three points bB
and C by the clutch D, and a distortion from its proper position rendered impos-
sible. All these points are thrown up out of the way of the projecting portions of
the aerodrome at the instant of release. This result is accomplished as follows:
when the car has reached the proper point in its forward course, the cam EF, which
is hinged at 1, is depressed by a roller fixed to the framework of the device. In
this motion it pushes down the adjustable connections FF’, which are attached at
their lower ends to the bell-erank arms GG, which turn about a central pivot at
2. Thus the downward movement of the connections FF’ opens the jaws of the

110

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 111

clutch D. While the clutch D is rigidly attached to G to prevent transverse
movement, it is hinged to the latter at 3 so that it can fold in a longitudinal di-
rection. Serewed to the clutch D is a narrow plate 4, which, when the clutch is
closed, is behind the lug 5, thus preventing any turning about the hinge 3.

But when the arms of G and the jaws of the clamp are thrown out by the
depression of F, the plate 4 is moved out from behind the lug 5 and the clamp
is free to fold to the front. The strut, hinged at 6, is under a constant tension
from the spring 7 to fold up, and is prevented from doing so only by the connec-
tions 8, by which it is held down until the release of the plate 4 from behind the
lug 5, when the spring snaps them instantly up and out of the way.

As the struts BB have no fixed connection with the aerodrome, they are re-
leased by the relaxation in the rigidity of the other connections and are thrown
up by their spring 9 and held in that position by the clip 10 catching beneath the
upper cross-piece.

The power for the propulsion of the car is obtained by means of from one
to nine helical springs working under tension, and multiplying their own mo-
tion four times by means of a movable two-sheave pulley, as shown in the
drawing.

Description or ABRODROME No. 5

When the details of the aerodrome, whose description is to follow, are con-
sidered from the standpoint of the engimeer accustomed to make every pro-
vision against breakage and accident and to allow an ample factor of safety in
every part, they will be found far too weak to stand the stresses that were put
upon them. But it must be remembered that in designing this machine, all
precedent had to be laid aside and new rules, adapted to the new conditions, ap-
plied. It was absolutely necessary, in order to insure success, that the weight
should be cut down to the lowest possible point, and when this was reached it
was found that the factor of safety had been almost entirely done away with,
and that the stresses applied and the strength of material were almost equal.

The same observation holds true of the boilers, aeolipile, and engines, when
regarded from the point of view of the economical generation and use of steam.
It was fully recognized that the waste of heat in the coil boilers was excessive,
but as it was necessary that there should be an exceedingly rapid generation of
steam with a small heating surface, this was regarded as inevitable.

In the engine the three points aimed at in the design were lightness, strength
and power, but lightness above all, and necessarily in a degree which long
seemed incompatible with strength. No attempt was made to secure the re-
quirements of modern steam-engine construction, either in the distribution of the
steam or the protection of the cylinder against the radiation of heat by a suitable
jacketing. The very narrow limits of weight permissible required that the bar-

Te, SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

rel of the cylinder should be as thin as possible, that no protective jacketing
should be used, and that the valve motion should be of the simplest description.
To obtaining the greatest lightness consistent with indispensable power, every-
thing else was subordinated; and hence, all expectation of ordinary economical
efficiency had to be abandoned at the outset.

It was only after long trials in other directions that Mr. Langley intro-
duced the aeolipile device, which for the first time provided sufficient heat. Even
in the aeolipile, however, it was apparent that nothing short of the most com-
plete combustion accompanied by the highest possible temperature of the flame
would be sufficient for the extreme demand. To secure this result under all
conditions of wind and weather, with the aerodrome at rest and in motion, re-
quired the long series of experiments that are given in another chapter. In
respect to the generation of heat, then, it is probable that it would be difficult to
exceed the performance of the final type of burner in practical work, but in the
utilization of this heat in the boiler, as well as in the utilization of the steam
there generated, the waste was so great as to be prohibitive under ordinary
conditions. But this was not ordinary work, and the simplest protection against
radiation from boiler, separator, and engine could not well be used.

The framework of the aerodrome is made of thin steel tubes, the main or
midrod extending the whole length of the machine and carrying the attach-
ments to which the wings are fastened. Suspended from this midrod by rigid
connections is a skeleton hull of steel tubing, shaped somewhat like the frame-
work of a boat, from which, directly abeam of the engines, arms are run out
like the outriggers of a rowboat for carrying the propellers. Within this cen-
tral hull are placed the aeolipile, the boiler, and the engine, which with their
auxiliary parts, the pump and the separator, constitute the entire power-gener-
ating apparatus.

The aeolipile consists of four essential parts: the spherical air chamber con-
taining the supply of compressed air by which the gasoline in the reservoir
tank is foreed into the burner; the reservoir tank containing the gasoline that
is to be used as a fuel; the gas generator wherein the liquid gasoline is heated
and converted into gas; and the burners where it is finally utilized to heat the
boilers.

The air chamber D, Plate 25, is a spherical vessel 120 mm. in diameter, lo-
vated at the extreme front end of the hull. It is made of copper 0.25 mm. thick
and has two openings. The front opening has a copper pipe 1 em. outside diam-
eter, to which the air pump for charging the chamber is connected. From the
back a copper pipe 5 mm. outside diameter extends to the top of the gasoline
reservoir.

This reservoir, shown at 7, Plate 25, is also a light, hollow sphere 120 mm.
in diameter; both this and the air chamber being made by soldering hemispheres

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of copper together at their circumferences. There are three openings in the
reservoir tank; two at the top and one at the bottom. One of those at the top
serves for the admission of the 5-mm. pipe bringing compressed air from the
air chamber; the other is connected with a pipe 1 em. in diameter, through which
gasoline is supplied to the tank, and which is closed by a simple plug at the top.
The hole in the bottom serves as the outlet for the gasoline to the burners. Close
to the bottom of the tank there is placed a small needle valve, which serves to
regulate the flow of oil, for, were the pipe left open, the compressed air would
force the oil out with such rapidity that the burners would be flooded and the
intensity of the flame impaired. The construction of this valve is clearly shown
in Plate 26A. It consists of a brass shell having one end (a) soldered to the bot-
tom of the tank. The needle enters through a stuffing box whose gland is held
by two small screws. The stem of the needle is threaded and engages in a thread
cut in the body of the casting and is operated by a fine wire on the outside. It
will readily be seen that this device affords a means of making a very accurate
adjustment of the flow of the liquid to the burners.

After leaving the needle valve the gasoline flows along the pipe S, Plate 25,
until it reaches the evaporating coil, VN. In order to subject the oil to as large
a heating surface as possible, in comparison with the sectional area through
which it is flowing, the pipe, which left the needle valve with a diameter of 6 mm.
soon contracted to 5 mm., is here flattened to a width of 7 mm. and a thickness
of 2mm. There are seven complete turns of this flattened tubing coiled to an out-
side diameter of 30 mm. At the end of the seventh coil the pipe is enlarged to a
diameter of 1 cm. and two coils of this size are added, the inside diameter being
the same as that of the flattened coil. This enlarged portion serves as a sort of
expansion chamber for the complete gasification of the gasoline, which is then
led back through a turn of the enlarged pipe, beneath the coils and to the front.
At the front end of the coil a small branch is led off, forming a ‘‘ bleeder,’’
which takes sufficient gas to supply the burner by which the coil is heated, the
products of whose combustion pass into and between the coils of the boiler
like those of the regular heating burners. The gas pipe rises in front of the coil
and by a 7’ connection branches to the two burners that are placed in front of
the coils of the boiler. These burner pipes are 5 mm. in diameter and enter
sheet-iron hoods forming regular burners of the Bunsen type, which are fully
shown in all their details in the accompanying engraving, Plate 26. The pipe is
plugged at the end, and a hole 0.9 mm. in diameter drilled for the nipple of the
burner in front of the coil where the water first enters from the separator, and
0.85 mm. for the one in front of the return coil. The face of the burner shell
stands exactly central with and 41 mm. in front of the coils.’

1Very exact accuracy in these minute details is indispensable to the efficient working of the
engines.

114 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOLe et

This constitutes the heat-generating portion of the machine, and with it it
is probable that a flame of as high a temperature is produced as can be reached,
with the fuel used, by any practical device.

The boiler or steam-generating apparatus may be said to consist of three
parts: the separator, the circulating pumps, and the generating coils.

The separator (M in Plate 25) is a device which has attained its present
form after a long course of development. As at present constructed, it is formed
of a hollow sphere 190 mm. in diameter and is located as nearly as possible over
the center of gravity of the whole apparatus. It serves the double purpose of

»? on aceount of

water reservoir and steam drum, and is called a ‘‘ separator
the function which it performs of separating the water from the steam as it en-
ters from the coils. There is a straight vertical pipe 10 mm. in diameter rising
from the top of the sphere and fastened to the right-hand side of the midrod.
This is used for filling the separater with water. Upon the other side of the
midrod there is a small steam dome 42mm. in diameter with a semi-spherical
top rising to a height of 70mm. above the top of the sphere. From this dome
two steam pipes are led off, one to the engine and the other to the steam gauge.

As already stated elsewhere, it was found in the experiments with the coil
boiler that an artificial forcing of the circulation of the water was a necessity,
as the natural circulation was too slow to be of any service. Accordingly, but
only after numerous devices involving less weight had failed, a pump driven
from the engine shaft was designed and used. In the early experiments vari-
ous types of pumps were tried in which the valves were opened and closed au-
tomatically by the pressure of the water. It was found, however, that with the
mixture of steam and water to be handled, the valves could not be depended
upon to open and close properly at the high speeds at which it was necessary to
run the engine. In Aerodrome No. 5, therefore, a double-acting pump with a
mechanically operated valve was used. The pump, shown in detail in Plate 264,
is driven from a shaft connected with the main engine shaft by a spur gear and
pinion, which rotates at half the speed of the engine shaft. The pump itself
consists of two barrels, the main barrel having a diameter of 23mm. with a
piston stroke of 20mm. The outer shell of the barrel is made of aluminum
bronze and is lined with a cast-iron bushing 1.25 mm. in thickness. The piston
has a length of 14mm. and is formed of an aluminum dise and center, having a
follower plate of the same material with two cast-iron split rings sprung in.
The water is received into and delivered from the valve cylinder, which is 18
mm. in diameter and also lined with a cast-iron bushing 1.25mm., thick. The
aluminum bronze shells of both cylinders are 0.75 mm. in thickness. The valve
is a simple piston valve 35 mm. long with bearing faces 4mm. long at each end.
The water is taken from the bottom of the separator and led to the center of the
valve chest of the pump by a copper p pe lem. outside diameter. The ports

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 115

leading from the valve to the main cylinder are 38mm. wide and 34 mm. apart
over their openings. It will thus be seen that when the valve is in its central
position, as it should be at the beginning of the piston stroke, both ports are
covered with a lap of 0.5mm. inside and out, so that the valve has to move
0.5mm. before suction or discharge can take place. As the valve is moving most
rapidly at this point, it opens and both functions begin before the piston has ad-
vanced perceptibly. The delivery is made at the ends of the valve cylinder
through two copper pipes of lcm. diameter that unite into a single pipe before
reaching the boiler. The throw of the valve is 14mm. so that the ports are un-
covered and held wide open for the greater portion of the stroke of the piston,
and begin to close only when the latter approaches the end of its stroke. In this
way perfect freedom is given to the flow of the water and all choking is avoided.
As the engine has been run at a speed of more than 688 revolutions per minute,
the pump must have made at least 344 strokes in the same time, thus displa-
cing 166.2 ee. of water. The diameter of the piston rod and valve stem is 3 mm.
and they pass through stuffing boxes with glands of the ordinary type for pack-
ing. This pump served its purpose admirably, and with it it was possible to
Maintain a continuous circulation of water through the two coils of the boiler.

The third element in the steam-generating system is the boiler proper *
(Plates 25 and 26A), which consists of two coils of copper pipe, having an out-
side diameter of 10 mm., each coil being formed of 21 turns each 75 mm. in di-
ameter upon the outside and spaced 7.5mm. apart, so that the total axial length
of each coil is 36 cm.

The water is delivered to the front end of the right-hand coil, and, first
passing through this, crosses over at the rear of the boiler to the left-hand
coil, returning through it to the front whence it is led to and delivered into the
top of the separator. Here the steam and water are separated, the former
going through the separator and thence to the engine, while the unevaporated
water falls to the bottom to be again taken into the pumps and sent through the
coils.

In order that the draft of the burner and the gases of combustion might not
be dissipated, it was necessary to sheathe the boiler. The method of doing this
is shown in Plate 25. It will be seen that the front half of the boiler is wrapped
in a sheet of mica through which the coils can be faintly seen. This, in turn, is
held at the extreme front end by a strip of thin sheet-iron, O. Over the back
end the stack Q, made of very thin sheet-iron, is slipped. This has an oblong
cross-section at the lower end where it goes over the boiler; it is provided with
a hole through which the midrod passes, and terminates in a circular opening of

about 10 em. diameter.

2The reader who may care to note the evolution of this boiler, by trial and error, will find a
portion of the many discarded types shown in Plate 13.

116 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

The engine, which is clearly shown in the dimensional drawing, Plate 26B, is
of the plain slide-valve type, using a piston valve and solid piston, without pack-
ing rings. The cylinder is formed of a piece of steel tubing 35 mm. outside di-
ameter, with flanges 47 mm. in diameter and 2.25 mm. thick brazed to each end,
to which the cylinder heads are attached by small machine screws. Inside this
eylinder is a thin cast-iron bushing in order to obtain a better rubbing surface
for the piston. The cross-head is a small piece of aluminum bronze, running on
round guides that also serve as cylinder braces. There are also four hollow
braces, 5 mm. in diameter, running from the back cylinder head to a corru-
gated steel bed-plate, that stands vertically and reaches from one side rod of
the frame of the hull to the other, and to which are bolted the bearings of the
main shaft. The connecting rod has the cross-section of a four-rayed star and
drives a crank in the center of the shaft. The following are some of the princi-
pal dimensions of the engine:

millimetres.
Inside «diameter sof ‘cylinder. .<ciais see nievalenicloieie eile eles 33
Stroke: of, MIStons ve ceech eee clos Meelcte hc tolsicls hee one Gienrreveseieteteyays 70
ene th of cylinder dnside@y~.sca-crcraecieren Gielrenicin serene eis 88
Tengeth: (of “piston stasis cis ccisa's ore is eraleya sie elohoeievateicloval eistalcise 11
Clearance: atiieacheend ic fo wicyancis ion here cies oat eeteie ener 0.5
Diametersok piston) ods saricyeyeeteecia iter letters 5
ength' Of Grosschead sir <..2 cr erterlariere ote creer serene 17.5
Diameter: «of “euides:. caves cle acarecd aw carter tarlarels stele cfereteeee 4.5
Distance from center to center of guides.................. 26
Menethyok ‘ewidesi a5 so Meh cocoate eee tered Oe aoe eine ee oe 110
Menzthiol wxrist-pin bearings. ss. cscers etetee eee oie aioeinte 8.5
eneth” of conneetin Sy TO dn iecicre cle ci oeversrare tele stetatoe oe iterates 150
Ratiovol connecting wrod) to strokes eee eee eerie 21/7 to 1
Length! of (erank=pinisi coats sere nai overs yyerern si aeel a) ratte otrseee erat al 10
Diameter of main shaft: i./5.c2 << 2's moots) <leielaleaterns tse ates (sie eile 8
Mength! of smain bearings 4/2. ctu-yerosrcleiecisiele sseret sieges este etter 25
Distance from center of cylinder to center of valve stem.. 35
engeth iol wWalveicc ok cidcree etetocsye ote toteleie hr lskeeasyersrerorstec eared 72
WAG: WOE POLES ys. ee. 5 tavecsigrevaherais-suareyatalttevararoye ietehena yoyelsteveueuele eietee rete 2
Outside lap ofsvalvers ct cet sais Soe cole Eee eae 4
Inside rlap».of svallvie i -vcratas wet tye cc areves vege ereieaciereicte, yar hctenet ersten 3)
Ms@ad’ Of” Valves). .3.3sAoveics etercys isis iors cveisre’s ele ieleie eievancveeienactersle Sie ote 0
Travel of valve...... See ODIO OI OL DUN OCA ORC OLITO tid Sr: 8 6 13
Cut-off from beginning (of Stroke). cic crcleseriec «fclslesercaeieic elie 57
PSXHAUSt /OMCISne aa eeieicec oe tote ete eieter eee cier oesaters te meet ereeh toes End of stroke
Exhaust ‘closes on return stroker ccna... et ante « servieieee aes 48
Diameter’ Of -valvecstemisicc:. ec, ccccessiere clsvote se tetese sce oreae revere erate 4.5
Diameter! (of CeCemunicey rice <teveratacateie te etoeresoiserercee verte etal 36
Width, (Of seCCOnUniC scorn ccc arcien ic Guster eciee oe neee Cee 4
Width of cramicanmi ss. .cyer tl otsic,siesierole s eters sy eeakevteteteretere ereveiete 0 4

The weights were nearly as follows:

grammes
10-9 00 re eee Cem Co oroOT COS nO Gf Onan OmGh Shot 464
Pump and! pumipShahtss arson crovarn cystotereenraieter ste rete oktions ce incre roe 231
yasoline itank and! Valvest asc iac. teprciet miele enfin sin ele aie 178
BUIMers® | £0, calek Setre-ciohatercueneuets inverse Ia Tee Sa ee ere 360
Boilers, frames holding boilers, and mica covers over boilers 651
Separator, steam gauge and pipe for engine................ 540
exhaust PlPes fs Secsicrc cise areteyaiayeLovureversiorslelere’ etsy etaiaiatate. comtelstatetets 143
Smoke ‘stack: 5.0.5.5 clas cic. svaieccse okele- cols (o/s tesla Oleye lol wvaseleheiviahete males 342

In all, 2909 grammes, or 6.4 pounds.

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 117

These weights are those determined in December, 1896, when some slight
changes had been made from the conditions existing at the time of the flight by
this aerodrome on May 6. Previous to that time, with a pressure of 130 pounds,
between 1.1 and 1.25 horse-power was given on the Prony brake. At the actual
time of flight the pressure was about 115 pounds, and the actual power very
nearly 1 horse-power.

The valve stem was pivoted to the center of the valve partly because this was
the lightest connection that could be made, and partly to allow the valve per-
fect freedom of adjustment upon the seat. Many parts, such as guides, braces,
erank-pins, wrist-pin and shafts, are hollow. The steam is taken in at the front
end of the steam chest, and the exhaust taken out of the center, whence it is led
back to the stack and by means of a forked exhaust pipe discharged in such a
way as to assist the draught of each coil of the boilers. Like the cylinder the
steam chest is made of a piece of steel tubing, 20mm. diameter on the outside,
with an inside diameter of 19 mm., and is fitted with a cast-iron bushing 0.5 mm.
thick, making the inside diameter of the steam chest 18mm. It, too, has flanges
brazed to the ends, to which the heads are held by small machine screws.

The shaft for conveying the power to the propeller shafts extends across
the machine from side to side; it is hollow, being 8mm. outside diameter, with
a hole 5mm. diameter through the center.

It is formed of five sections: the middle section, containing the crank, has
a length of 110mm. and is connected at either end, by flanged couplings, to
lengths 320mm. long, which are in turn extended by the end sections having a
length of 230mm. In addition to the four main bearings that are bolted to the
pressed-steel bed-plate already mentioned, there are two bearings on the outer
framework on each side. At the outer end of each shaft there is keyed thereto
a bevel gear with an outside diameter of 27 mm. and having 28 teeth. This gear
meshes with one of 35 teeth upon a shaft at right angles to the main shaft and
parallel to the axis of the aerodrome. These two shafts, one on either arm,
serve to carry and transmit the power to the propellers. They are 192 mm. long,
8mm. in diameter, and are provided with three bearings that are brazed to a
corrugated steel plate forming the end of the outrigger portion of the frame.
These shafts are also hollow, having an axial hole 4mm. in diameter drilled
through them. The propeller seat has a length of 43mm. and the propeller is
held in position by a collar 25mm. in diameter at the front end, from which
there project two dowel-pins that fit into corresponding holes in the hubs of the
propellers, which are held up against the collar by a smaller one screwed into
the back end of the shaft. The thrust of the collar is taken up by a pin screwed
into the end of the forward box and acting as a step against which the shaft
bears, the arrangement being clearly shown by the accompanying drawing,

Plate 26A,
12

118 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vot. 27

This, then, comprises the motive power equipment of the aerodrome, and,
to recapitulate, it includes the storage, automatic feeding and regulation of the
fuel; the storage, circulation and evaporation of the water; the engine to con-
vert the expansive power of the steam into mechanical work; and the shafting
for the transmission of the energy developed by the engine to the propellers.

The propellers were made with the greatest care. Those used in the suc-
cessful trials were 1 metre in diameter, with an actual axial pitch of 1.25 metres.
They were made of white pine, glued together in strips 7mm. thick. The hub
had a length of 45 mm. and a thickness or diameter of 25mm. At the outer edge
the blade had a width of 315mm. and a thickness of 2mm. These propellers
were most accurately balanced and tested in every particular; each propeller
blade was balanced in weight with its mate and the pitch measured at every
point along the radius to insure its constancy; finally the two propellers of the
pair to be used together were balanced with each other so that there would be
no disturbance in the equilibrium of the machine. As will be noted from the
foregoing description of the machinery, the propellers ran in opposite direc-
tions, as they were made right- and left-hand screws. The weight of each pro-
peller was 362 grammes.

We now turn again to take up the details of the construction of the frame-
work by which this propelling machinery is carried. The whole aerodrome, as
clearly shown in the photographs, Plates 27A and 27B, is built about and depend-
ent from one main backbone or midrod, which extends well forward of all of the
machinery and aft beyond all other parts. This rod, as well as all other por-
tions of the framework, is of steel tubing. The midrod, being largest, is 20 mm
outside diameter, with a thickness of 0.5 mm. It is to this midrod that the
wings are directly attached, and from it the hull containing the machinery is
suspended.

The plan outline of the hull skeleton is similar to that of the deck of a ves-
sel. The steel tubing, 0.5 mm. thick, of which it is formed, has an outside diam-
eter of 15mm. from the front end to the cross-framing used to carry the pro-
pellers, back of which the diameter is decreased to 10 mm.

The midrod makes a slight angle with this frame, the vertical distance be-
tween the centers of the tubing being 73mm. at the front and 67mm. at the-
back. The tube, corresponding to the keel of a vessel, is braced to the upper
tubes by light U-shaped ribs and by two 8-mm. tubes forming a V brace on a
line with the back end of the guides of the engine. At the extreme front and
back there is a direct vertical connection to the midrod.

The propeller shafts are 1.23 m. from center to center, and are carried on
a special cross-framing, partaking, as already stated, of the character of an out-

‘jgger ona row-boat. (See Plate 27B.) The rear rods, which are of 10 mm. steel
tubing, start from the front end of the rear bearings of the propeller shaft and

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 119

extend across from side to side. The top rod is brazed to the side pieces of the
hull and the bottom rod to the keel. They are connected by a vertical strut of
8mm. tubing at a distance of 265mm. inside of each propeller shaft. At the
front end of the propeller shaft two more rods run across the frame. The lower
is similar and parallel to the back rod already deseribed, while the upper is bowed
to the front, as shown in the plan view of the frame (Plate 30). In order to
take the forward thrust of the propeller a second cross-brace is inserted, which
runs from the rear bearing of the propeller shaft to a point just in advance of
the front head of the cylinder, and is brazed to the two upper tubes of the cross-
frame as well as to the upper tubes of the main framing of the hull. The outer
ends of the tubes of the cross-framing are brazed to a thin, stamped steel plate
which firmly binds them together, while at the same time it forms a base for
attaching the bearings of the propeller shaft. This end plate has a thickness of
one millimetre.

In addition to the framing proper there are two guy-posts which fit imto
the sockets CC, and over which truss wires are drawn, as shown in the side view
in Plate 27A. These posts have a length of 730 mm. from the lower edge of the
socket, and are capped at their lower extremity by a light steel ferrule whose
outside diameter is 10 mm.

From the drawing of the wings of No. 5, shown in Plate 17, it will be seen
that they are formed of two pine rods 15mm. in diameter at the inner ends, ta-
pering to a half circle of the same diameter at the tips. These rods are con-
nected by eleven spruce ribs measuring 8mm. 3 mm., and curved, as shown in
the side elevation, these, in turn, being covered by a light white silk drawn so
tightly as to present a smooth, even surface. The total length of the wing is 2
metres, and the width over all is 805 mm. Vertical stiffness is obtained in the
wings by a series of guy-wires, which pass over light struts resting upon the
main rods. These main rods are inserted and held in the wing clamps 4 and B,
Fig. 16, and make an angle of 150° with each other. As is the case with all
other essential details of the aerodrome, a great deal of time and attention was
given to the designing of the wing clamps before a satisfactory arrangement
was secured.

To enable it to control the aerodrome in both directions, the tail-rudder,
Plate 27A, has both a horizontal and a vertical surface, the approximate dimen-
sions of which are, length 115 em. (3.8 feet), maximum width 64 em. (2.1 feet),
giving each quarter section an area of about 0.64 sq.m. (6.9 sq. ft.). It is given
the proper angle and degree of elasticity in a vertical direction by the flat hick-
ory spring, which fits into the clamp N, and attaches the rudder to the frame.

The only other attachments of the aerodrome are the reel, float, and counter.
They have nothing whatever to do with the flying of the machine, and are

120 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

merely safety appliances to insure its recovery from the water. The reel con-
sists of a light spool on which a fine cord is wound, one end of which is attached
to a light float that detaches itself and lies upon the surface of the water when
the machine sinks, while the other end is fastened to the spool that goes down
with the aerodrome. The ‘float ’’ is a light copper vessel with conical ends
which is firmly fastened to the midrod, and which is intended to so lower the
specific gravity of the whole machine that it will not sink. The cylindrical por-
tion of this float has a length of 250mm. and a diameter of 170 mm., one cone
having a length of 65mm. and the other and front one a length of 140 mm.,
which makes the total length of the float 375mm. It is made of very thin cop-
per, and served in the successful trials not only as a float to sustain the machine
on the surface of the water, but also as a weight by which the center of gray-
ity was so adjusted that flight was possible.

The counter records the number of revolutions of the propellers after
launching. It is a small dial counter, reading to 10,000, with a special attach-
ment which prevents any record being made of the revolutions of the propellers,
until the actual moment of launching, when a piece on the launching apparatus
throws the counter in gear at the instant that the aerodrome leaps into the air.

Description or AgRopROME No, 6

Aerodrome No. 6, it will be remembered, was the outgrowth of a number of
changes made in No. 4 during the fall of 1895 and the early part of 1896. In
this reconstruction the aim was to lighten the whole machine on account of the
smaller engines used on No. 6, and to arrive at better conditions as regards sta-
bility than existed in either No. 4 or No. 5. The modifications from No. 4 were
so radical and the differences that exist between Nos. 5 and 6 are so consider-
able as to demand careful attention.

As regards general appearance the frame of Aerodrome No. 6 resembles
that of No. 5 in consisting of a single continuous midrod of steel tubing, 20 mm.
in diameter, 0.5 mm. thick, immediately beneath which the hull containing the ma-
chinery is situated. In reconstructing the framework after the tests in Janu-
ary, 1896, had shown it to be dangerously weak, especially against torsion, it was
decided to make the hull only strong enough to carry its contents and to attach
it to the stronger midrod in such a way that all torsional strains would be taken
up by it, whereas in No. 5 the hull structure must bear a large proportion of
such strains. It was therefore built throughout of 8-mm. tubing, 0.8 mm. thick,
and was rigidly attached to the midrod by braces at the front and rear, and also
at the eross-frame. The hull was also made narrower (except at the rear, where
it was widened to contain the boiler) and shorter than the hull of No. 5—an ad-
vantageous change made possible by the fact that the engines were not contained
in the hull, but mounted on the transverse frame.

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In No. 5, as described above, a single engine mounted at the front end of the
hull communicated its power through transmission shafts and gearing to the
propellers, which were necessarily in the same plane. This brought the line of
thrust very nearly in the same plane as the center of gravity of the aerodrome,
a condition tending to promote instability of longitudinal equilibrium. In No.
6, however, the use of two engines situated on the transverse frame and com-
municating their power directly to the propellers, made it possible to raise the
transverse frame 12em. above the hull, and thus raise the line of thrust to a
position intermediate between the center of pressure and the center of gravity,
without materially affecting the latter. As a result of this change Aerodrome
No. 6 was rendered much more stable and made steadier flights with fewer un-
dulations than No. 5.

The engines in use on No. 6 were the small engines described above in con-
nection with No. 4. The cylinders were of steel tubing 2.8 em. in diameter, with
a 5-em. stroke, each cylinder thus having a capacity of 30.8 ce. They were lined
with a thin cast-iron bushing and cast-iron rings were sprung in the piston head
so as to give as smooth a rubbing surface and as perfect action as possible. As
in the engine of No. 5 a plain sliding valve of the piston type was used, cut-off
being approximately at one-half, though the ports were so small that it was diffi-
cult to determine it with any great accuracy. No packing was used, but the
parts were carefully ground so as to give a perfect fit.

These engines, as is most clearly shown in Plate 30, were mounted sym-
metrically on either side of the cross-frame and were connected directly to the
propeller shafts. In order to insure that the propellers would run at the same
rate, there was provided a synchronizing shaft, 7’, in Plate 30, having on each
end a bevel gear, which intermeshed with similar gears on the propeller shafts.
Steam for the cylinders was conveyed from the separator through the pipes LL.

The steam-generating apparatus for No. 6 was exactly like that already de-
seribed in connection with No. 5, the only difference being in the more compact
arrangement in the case of No. 6. The relative location of the apparatus in the
two models is clearly shown in Plates 28, 29B, and 30, the corresponding parts be-
ing similarly labeled, so that a separate description for No. 6 is superfluous.

The wings used on No. 6 were somewhat smaller than those of No. 5, and
differed from them in having the front mainrib bent to a quadrant at its outer
extremity and continued as the outer rib of the wing. The degree of curvature
of the wings was also somewhat less, being one-eighteenth for No. 6 and one-
twelfth for No. 5. The four wines were of the same size and had a total area
of 54 sq. ft. On account of the shortened hull of No. 6 they were allowed a
much greater range of adjustment, which rendered it much easier to bring the
CP into the proper relative position to the CG than was the case with No. 5.

122 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. .27

The Pénaud rndder for No. 6 was similar to that for No. 5, the two in fact
being interchangeable, and was similarly attached to the frame. The reel, float,
counter, and all other accessories were identical for the two machines.

To sum up the comparative features of these two successful steam-driven
models: Aerodrome No. 6 was both lighter and frailer than No. 5, and required
much more delicate adjustment, but when the correct adjustments had been made
its flying qualities were superior, as regards both speed and stability.

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Part Il. 1897 To 1903
By CHARLES M. MANLY

Assistant in Charge of Experiments

CHAPTER I
INTRODUCTORY

Although in 1896 Mr. Langley had made the firm resolution not to under-
take the construction of a large man-carrying machine, as he realized that his
multitudinous administrative duties left him practically no time available for
original research, yet the longing to take the final great step of actually trans-
porting a human being through the air, which the successful flights of the mod-
els had now for the first time in the history of the world actually proved to be
possible, soon became irresistible.

Ten years of almost disheartening difficulties, a full appreciation of which
can hardly be gained from the preceding description, had already been spent in
demonstrating that mechanical flight was practicable, and Mr. Langley thor-
oughly realized that the construction of a large aerodrome would involve as
great, if not even greater difficulties. Nevertheless, his indomitable will, which
balked at no obstacle, however great it might seem, prevailed against the ad-
vice of his close friends and associates, and even that of his physician, who had
counselled him that a resumption of concentrated thought and vigorous en-
deavor would materially shorten his life, which had already passed three score
years. Only a few were privileged to come into close contact with him in his
daily work, and thereby catch the inspiration of his unwavering persistence, his
ceaseless perseverance, his plain inability to submit to defeat; but no one who
has read the record of his astronomical expedition to Mt. Whitney, or the story
of his development of the Bolometer, or the preceding chapters of this history
of his years of patient work in the development of the flying machine, can have
failed to obtain some appreciation of this most striking feature of his character.
Having once determined on the accomplishment of a definite object, no amount
of difficulty that might arise deterred him from pushing on until in some way
and by some means he had succeeded; and no one appreciated better than he
that if the thin edge of the right wedge can be inserted under an obstacle, that
obstacle can be removed, no matter how formidable it may seem.

The undertaking of the construction of a large aerodrome was very largely
influenced by President McKinley, who had become impressed with the great

123

124 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

possibilities of a flying machine as an engine of war. When he found that Mr.
Langley was willing to devote his own time to the development of a machine,
provided the Government would furnish the funds for the actual construction
and tests of it, he appointed a joint board, consisting of Army and Navy offi-
cers, to investigate and report on the plans with which Mr. Langley had achieved
success with the models. The report of this joint board of Army and Navy
officers being favorable, the Board of Ordnance and Fortification of the War
Department, at the direction of President McKinley, requested Mr. Langley to
undertake the construction and test of a machine, which, while not expected to
be a practical war machine, might finally lead to the development of such an en-
gine of war. In this connection it is interesting to read a letter which Mr. Lang-
ley addressed to the Board of Ordnance and Fortification at the time he un-
dertook this work.

SmirHsontan Institution, December 12, 1898.

The Board of Ordnance and Fortification, War Department.

GENTLEMEN: In response to your invitation, I repeat what I had the honor
to say to the Board—that I am willing, with the consent of the Regents of this
Institution, to undertake for the Government the further investigation of the
subject of the construction of a flying machine on a scale capable of carrying a
man, the investigation to include the construction, development and test of such
a machine under conditions left as far as practicable in my discretion, it being
understood that my services are given to the Government in such time as may
not be oceupied by the business of the Institution, and without charge.

I have reason to believe that the cost of the construction will come within
the sum of $50,000.00, and that not more than one-half of that will be called for
in the coming year.

I entirely agree with what I understand to be the wish of the Board that
privacy be observed with regard to the work, and only when it reaches a suc-
cessful completion shall I wish to make public the fact of its success.

T attach to this a memorandum of my understanding of some points of de-
tail in order to be sure that it is also the understanding of the Board, and I am,
gentlemen,

With much respect,
Your obedient servant,
S. P. Laneuey.

MemoranpuM

ATTACHED TO MY LETTER OF THIS DATE TO THE BOARD OF ORDNANCE AND FORTIFICATION

While stating that I have, so far as I know, an exclusive right of property
in the results of the experiments in aerodromics which I have conducted here-
tofore and am now conducting, and while understanding that this property and
all rights connected with it, whether patentable or otherwise, will remain mine
unqualifiedly, T am glad to place these results, without charge, at the service of
the Board of Ordnance and Fortification for the special construction at present
proposed, which seems to me to be of National utility.

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 125

I assume that no public statement will be made by the permission of the
Board until the work is terminated, but that I may publish ultimately at my
discretion a statement of any scientific work done in this connection.

I understand that the exercise of this discretion includes the ordering and
purchase of all material by contract or in open market, and the employment of
any necessary help, without restriction, and that, while I desire that no money
shall pass through my hands, itemized bills for each expenditure, made in proper
form and approved by me, will be paid by the Chief Signal Officer.

Much has already been spent at the Smithsonian Institution for the pur-
pose in question, in special apparatus, tools and experiments, and in recent
constructions now actually going on, which have involved still more time than
money, and which are essential for experimental use in building the proposed
machine; and since to re-create all this independently would greatly defer prog-
ress, | assume that my discretion includes the decision as to how far this shall
be used and paid for at the cost of this allotment (it being understood that I
have no personal property in any of the material which might be transferred for
the purpose of the work) ; and I also assume that my discretion includes the de-
cision as to where the work shall be conducted—that is, whether in shops al-
ready constructed, or in others to be elsewhere erected or rented, with the nee-
essary adjuncts, whether on land or water, and generally whatever is necessary
to the earlest attainment of the object desired by the Board.

S. P. Laneuey.
SmirHsonian Institution, WasHinctTon, D. C.,
December 12, 1898.

As is always the case in experimental work, especially in a field so very new
as was the field of aerodromics at the time that this larger construction was un-
dertaken, the ‘‘ plant,’’ or shops and laboratories required for the constructional
and testing work, grew to a size far beyond what seemed even remotely pos-
sible at the beginning of the work; and even the mere administration involved in
the carrying on of this work proved to be no inconsiderable matter before it had
progressed very far.

The years of experiment with the models had demonstrated clearly that the
greatest difficulty in the development of the aerodrome was the construction of
a suitable power generator, which should combine the elements of extreme light-
ness and unusual power with a fair degree of durability. Although remarkably
good results had been secured in the case of the models through the use of steam,
it was realized from the first that not only would the development of a steam-
power plant for a large man-carrying aerodrome present difficulties of a con-
structional nature, but that such a steam plant would necessarily be so fragile
and delicate as to make it a constant menace to the machine which it was to pro-
pel. The solution of the difficulty, it was believed, was to be found in the use of
an internal combustion engine; but Mr. Langley had had very little experience
with such engines, and was averse therefore to undertaking the construction of
a large aerodrome until he had assurance that a suitable gasoline engine could
be secured. Before making an agreement to attempt the work for the War De-

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126 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27
partment, he had, therefore, made a search for a reliable builder who would un-
dertake to construct a gasoline engine of not less than 12 horse-power to weigh
not exceeding 100 pounds, and what then seemed a safe contract had been en-
tered into with such a builder to supply one engine which would meet these
requirements.

Almost immediately before the Board of Ordnance and Fortification had of-
ficially placed the work in Mr. Langley’s hands and had made an allotment of
fifty thousand dollars to meet the expenses thereof, it was found that the en-
gine builder could not be depended on, and that it would, therefore, be neces-
sary to find one who was more reliable and more experienced in the construc-
tion of light engines. After a most extended search for the best builder to un-
dertake this work, a contract was entered into on December 12, 1898, with Mr.
S. M. Balzer, an engine builder in New York City. He was to furnish a twelve-
horse-power engine to weigh not more than 100 pounds, and delivery of it was to
be made on or before February 28, 1899. With this great problem of the engine
apparently provided for, every facility of the Institution shops was pressed to
the utmost limit in order to have the frame, supporting surfaces, launching ap-
paratus, and other accessories ready as soon as possible after the delivery of
the engine. It was expected from the first that more power would be necessary
than this one engine would furnish, and provision had been made in the contract
that a duplicate engine should be constructed immediately after the completion
of this first one. From past experience, however, it was not likely that the cor-
rect balancing of the aerodrome could be determined from a priori calculation
based on the results obtained with the models, and it was, therefore, expected
that the aerodrome would have to be launched several times before a successful
flight could be obtained. In view of this it was planned to make a test of the
machine as soon as the first engine was ready, with the expectation that, while
the aerodrome would not have sufficient power to fly, yet the test would furnish .
definite data on the all-important question of balancing, and also determine
whether or not the launching apparatus would require modification. In fact,
Mr. Langley felt so apprehensive that the first, and possibly the second test,
would be unsuccessful that, in order to avoid the possibility of a fatal accident,
it was planned that a dummy should be used to represent the weight of the
man in these preliminary tests.

This plan, however, was not carried out. In 1903, when the large aerodrome
was finally completed, so much time had been lost that the writer proposed to
assume the risks of such an accident and to guide the machine in its first test,
in the hope of avoiding a disaster, with the consequent delay of months for re-
pairs, which the presence of a controlling hand capable of correcting any inac-
curacies of balancing rendered far less likely to occur. To this proposal Mr.
Langley assented with great reluctance, as he fully realized the danger involved.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 127

Particular attention is called to the above facts, which clearly show that
while a certain degree of success in the initial tests was later hoped for, yet
from the beginning it had been felt rather certain that several tests would have
to be made before final success would be achieved.

To those experienced in scientific experiments this realization of the prob-
ability of several tests being necessary before success could reasonably be ex-
pected does not seem strange, for the record of past experience contains very
few examples of epoch-making inventions springing full fledged from the hand
of their maker and proving a success on the first test.

The two experiments made in the fall of 1903, in which the aerodrome was
each time so damaged in the process of launching that its ability to fly was
never really tested, should therefore be considered merely as the first of a se-
ries which it had been expected would need to be made before success would be
achieved. Further tests were made impossible at the time on account of the
lack of funds, the expense of such work being unusually heavy.

While the lack of funds, therefore, was the real cause of the temporary sus-
pension of the work, yet an influence which does not often enter into scientific
work—the unjust criticism of a hostile press—was directly responsible for the
lack of funds. It seems very certain that had it not been for this criticism of
the press the funds would have been readily forthcoming for continuing the
work to the point of success.

CHAPTER II
GENERAL CONSIDERATIONS

In the development of man-carrying flying machines two well-defined paths
are open. First: Starting with gliding machines, in which gravity furnishes
the motive power, the operator may by practice acquire sufficient skill in con-
trolling them to warrant the addition of propelling mechanism, and individual
skill in control may be gradually replaced by automatic controlling mechan-
ism. Second: From self-propelled models, possessing automatic-equilibrium
controlling mechanism, and of a sufficient size to furnish determinative data,
one may, by proper modification in size and construction, progress to an auto-
matically controlled man-carrying machine in which, for ideal conditions, no
especial skill on the part of the operator is required. Hach method has its
advantages.

After concluding his earlier and purely physical researches, the results of
which were embodied in ‘‘ Experiments in Aerodynamics,’’ Mr. Langley was so
firmly convinced of the practicability of mechanical flight that he undertook
the construction of the model aerodromes in order to demonstrate it. It is very
doubtful if at any time, prior to the successful flights of the models in 1896, he
seriously contemplated the construction of man-carrying machines. His object
in developing the models was not, therefore, to furnish a prototype for a large
machine, but merely to demonstrate the feasibility of mechanical flight ; and this
he did. This is shown very clearly by the closing remark of the article he pub-
lished in 1897, describing the flights of the models. ‘‘ I have now brought to a
close the portion of the work which seemed to be specially mine—the demon-
stration of the practicability of mechanical flight—and for the next stage, which
is the commercial and practical development of the idea, it is probable that the
71 When he later undertook the construction of the
large machine for the War Department it was natural that, with the mspiring
sight of the models in flight still fresh in his mind, he determined to use as a

world may look to others.

prototype these successful machines, which were the only things of human con-
struction that had ever really flown for any considerable distance.

Not being an engineer, and realizing that to pass from the construction of
models to that of man-carrying machines involved the solution of many engi-
neering problems, Mr. Langley, in the spring of 1898, sought the advice of Dr.
R. H. Thurston, who had from the first manifested the deepest interest in his

1“The Flying Machine” McClure’s Magazine, June, 1897.
128

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 129

work in aerodromics. On the recommendation of Dr. Thurston he engaged the
services of the writer, who assumed charge of the work in June, 1898.

While the method of ‘‘ cut and try ’’ had brought success in the models, and
was perhaps the only method by which they could have been successfully devel-
oped, it was thought that, with these models as a basis of design, much time
would be saved by making an analytical study of them as engineering structures,
and from the data thus obtained the proper proportions for the parts of the
larger machine could be calculated.

Such an analytical study, however, revealed very little from which to make
ealculations as to the strength necessary for the various parts of the large ma-
chine, but it did show very clearly that most of the parts were working under
stresses generally far above the elastic limit of the materials, and in many cases
the ultimate breaking strength was closely approached. Such a condition was
the natural outcome of the method by which these models had been developed—
all the various parts having been built at first of the least possible weight and,
when they proved too weak, strengthened until they would withstand the stresses
imposed on them. It is extremely doubtful if previous calculations as to the
strength necessary would have been of any assistance, in fact it is probable
that it would have been a distinct disadvantage and would have resulted in the
machines being entirely too heavy for flight.

The exact strength which had been incorporated in the frames of the mod-
els was as unknown as was the exact amount of the stresses which they had been
made to withstand. Their static strength was easily determined by calculation,
but the stresses due to the live loads were incapable of exact determination
from the available data, for stresses produce strains, which in turn generally
cause distortions accompanied by greatly increased stresses. While exact data
were, therefore, lacking as to stresses and strengths in many of the important
parts, yet the models furnished most important illustrations of unusual strength
for minimum weight, and a careful study of them showed many ways in which
increased strength could be obtained with decreased weight which could hardly
have been devised without these concrete examples.

It was, however, by no means possible to build the large aerodrome within
the permissible limits of weight by simply increasing the various parts of the
models according to some predetermined function of the size of the whole.

The fundamental difficulty is that inevitably, by the laws of geometry,
which are mere expressions of the properties of space, if a solid of any form is
magnified, the weight increases as the cube, while the surface increases only as
the square, of the linear dimensions. Successive generations of physicists and

mathematicians pointed out that while this ‘* law of the cube ”’

is of advantage
in the construction of balloons, yet it is a stumbling block that will prevent man

13

150 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

from ever building a dynamic flying machine sufficiently large to carry even one
human being.

However, since strength is a function of material and form rather than
weight, it is possible by selecting proper materials and adopting suitable struc-
tural forms to evade to a certain extent this ‘‘ law of the cube.’’? The whole his-
tory of structural science has therefore been a series of attempts to find stronger
and lighter material and to discover methods of so modifying form as to dis-
pense with all parts of a structure that do not contribute to its strength. So in
aerodromics the structural problem has been that of finding materials and forms
best suited to the purpose for which they are required, for it does not always
follow that either the form or the material best suited for one scale of construc-
tion is the most advantageous to employ on a different scale. Nor is even the form
or material which gives the greatest strength for the least weight necessarily
the best to employ. For the structural problem must necessarily be co-ordinated
with those of balancing, propelling, and transporting, and each must, therefore,
have its proper attention in the design of the whole machine.

Many of the general considerations of the design of an aerodrome suff-
ciently large to transport a man were determined during the spring and summer
of 1898, when the first actual drawings (Plate 32, Figs. 1, 2 and 3) of the pro-
posed machine were made. Starting with the assumption that the Models Nos.
5 and 6 were capable of transporting a load of approximately ten pounds more
than their weight, it was seen that, since the supporting surface of any aero-
drome would increase approximately as the square of the linear dimensions, in
order to carry a man the aerodrome would need to be approximately four times
the linear dimensions of these models. Calculations based on the results accom-
plished in the construction of the models indicated that such an aerodrome
would need to be equipped with engines developing 24 horse-power. The best
that could reasonably be hoped for was that these engines would not weigh over
200 pounds, and, therefore, allowing 40 pounds for fuel and fuel tanks, it be-
came necessary to bring the weight of frame, supporting surfaces, tail, rudder,
propellers and every other aecessory within 250 pounds, if the total weight of
the machine, including 150 pounds for the aeronaut, was not to exceed 640
pounds, or 16 times the combined weight of the model and its load of 10 pounds.
Although the problem of constructing the frame, wings and all other parts
within the limit of 250 pounds seemed indeed formidable, it was believed that the
ereatest obstacle in the production of such a machine would be that of securing a
sufficiently light and powerful engine to propel it.

2Qne noted astronomer and mathematician re-affirmed this opinion as late as 1900 and even
stated that man could not hope to construct a flying machine capable of sustaining a weight as

great as our largest birds, not knowing that even at that time the model Aerodromes Nos. 5 and 6
had already done more than this.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 32

TRANSVERSE SECTION

SIDE ELEVATION

SCALE
Oy ue sal, Nes) ie. im, ye) ay lore,
——————_——_ —

DRAWINGS OF PROPOSED MAN-CARRYING AERODROME, 1898

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 131

A brief account has already been given of the attempts made by Mr. Lang-
ley to secure a suitable gasoline engine for the large aerodrome, but the difficul-
ties encountered in the search have not perhaps been sufficiently emphasized.
At this time (1898) the automobile industry, through which has come the de-
velopment of the gasoline engine, was in its infancy, and there were few build-
ers either in the United States or Europe who were attempting anything but
rough and heavy construction. Many of them were enthusiastic over the possi-
bilities of the internal combustion engine, and were ready to talk of devising
such an engine as the aerodrome would require, but few were willing to guaran-
tee any such definite results as were demanded. However, the prospects of se-
curing a suitable gasoline engine from a reliable builder within a reasonable
time seemed so strong that it was decided early in 1898 to begin the construc-
tion of the frame on the general plan which would probably be best adapted for
use with a gasoline engine, and in ease it finally proved impossible to secure such
an engine, to construct later a steam plant which could be adapted to this par-
ticular frame.

Some tentative work on the construction of the frame was accordingly be-
gun in the summer of 1898, some months before an engine builder was found
who seemed likely to be successful in furnishing the engines. An extensive
series of tests on propellers was also made at this time for the immediate pur-
pose of determining what form and size would be best, since the dimensions of
the transverse frame could not be definitely settled until it was known how large
the propellers would need to be.

Preliminary designs were also begun for the wings, rudders, and launching
apparatus, but when the point was reached of actually making the working
drawings for these, it was seen that the change in the scale of the work re-
quired many important modifications in constructional details. As the models
had flown successfully only three times, and in each case under practically the
same conditions, it was felt that it would be unwise to make changes in im-
portant details without first making a series of tests of the models in flight to
determine the effect of such changes. It was therefore decided to completely
overhaul Models Nos. 5 and 6, strengthening them in many important parts and
‘‘tuning up ’’ their power plants, which had slightly deteriorated since they
were last used in November, 1896. When the work of preparing these models
for further experiments was begun it was thought that it would require at most
only a few weeks, but as it progressed it was found that certain parts of the
mechanical work on the engines had been so poorly executed originally that it
would be necessary to practically rebuild the engines. The final result was that
the power plants of both aerodromes were entirely rebuilt, and they were not
ready for actual test in flight until the spring of 1899,

132 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

Much of the preliminary work necessary for the determination of actual
working plans was therefore completed in the summer and fall of 1898, and when
on December 12 a seemingly satisfactory contract for the engines for the large
aerodrome had been made it was thought that rapid progress could be made on
the constructional work after January 1, 1899, when the allotment from the War
Department would become available.

CHAPTER IIT
EXPERIMENTS WITH MODELS

Immediately after the contract for the engine had been placed and the
actual work had been begun, attention was given to the problem of providing
means for properly launching the aerodrome. On the theory that the plan of
launching the small aerodromes, which had finally been adopted after many years
of painstaking experiment, would be the best to employ for the large aerodrome,
Mr. Langley decided to have constructed a large house-boat with the launching
track arranged on it in a way similar to that used for the small machines.
While the general plans for this boat had been under consideration for some
time, the actual working drawings were completed in January, 1899, and so
great seemed the need for expediting its construction, in order to have it ready
at the time when the engine was expected, that the contract which was made
for its construction specifically provided for its being completed promptly, there
being a large forfeit to cover any delay on the part of the contractor.

While the boat itself was being constructed, the working drawings were
completed for the house to be built on it, and a contract was made for the con-
struction of this house within a given period, there being also a time forfeit in
this contract.

When the end of February arrived, it was found that, although the engine
builder had succeeded in constructing an engine which weighed one hundred
pounds, and which theoretically should have given something over twelve horse-
power, yet he was unable to make it work properly. And then began a pro-
tracted period of most exasperating delays, the engine builder promising from
week to week that certainly within the succeeding ten days he would be able to
make delivery of the engine developing the full horse-power for which the con-
tract called. After this delay on the engine had continued for some months—
a delay which necessitated the cessation of the work on the main steel frame
of the aerodrome, as it was deemed best to make certain tests of the engine
running while supported by a portion of the frame to determine whether or not
it was strong enough before completing the rest of it—Mr. Langley decided to
employ part of the time in the construction of a model of one-eighth the linear
dimensions of the large aerodrome, which was to be used in testing a model of
the newly designed launching apparatus described later, and which might also
be flown as a kite in making check measurements on the proper balancing which

should be employed for the large aerodrome.
133

134 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

The perfected launching apparatus which had been used for the steam-
driven models Nos. 5 and 6 (deseribed in Part I, Chapter X) had proved most
satisfactory and reliable, but when the designs were made for a launching ap-
paratus for the large machine it was found that an exact duplication of the
plan of the small one involved serious difficulties in connection with the con-
struction of the house-boat, owing to the very considerable weight and size of
the turn-table necessary to permit the aerodrome to be launched in any desired
direction, regardless of the direction in which the house-boat might be pomting
under the influence of the wind and tide. A new design was accordingly made
for a launching apparatus in which the launching car was to run on a track
mounted directly on the turn-table, the launching car supporting the aerodrome
from underneath, instead of being mounted in an inverted position on an over-
head track with the aerodrome depending from it.

From the previous description of the launching apparatus, it will be re-
ealled that, in order to provide that the aerodrome should drop slightly at the
moment of its release from the car, and thereby avoid all danger of entangle-
ment, the speed of the launching car at the point at which the aerodrome was re-
leased was purposely made less than the ‘‘ soaring speed ”’ of the aerodrome.
Having this feature in mind, when designing the ‘‘ underneath ’’ launching ap-
paratus, it was recognized that the danger of the aerodrome becoming entan-
gled with this form of apparatus could be avoided by making the launching speed
greater than the velocity which it would be necessary for the aerodrome to
have in order to soar, provided the balancing was correct and the aerodrome did
soar. Nevertheless, it was deemed unwise to put too much dependence on the
empirical calculations from which the balancing of the large aerodrome would
necessarily be determined, and, therefore, some means seemed necessary for
causing the launching car to drop out of the way immediately upon releasing
the aerodrome. In the new design, more completely described below, in Chapter
TV, this was accomplished by so arranging a portion of the front end of the track
that, at the moment the launching car released the aerodrome, it dropped like a
disappearing gun carriage, leaving the aerodrome free in the air with no pos-
sibility of becoming entangled, provided the aerodrome itself did not drop more
rapidly than an angle of 15 degrees.

A small working model of this launching apparatus, one-eighth the linear
dimensions of that which would be necessary for the large aerodrome, was first
designed and constructed in the shop, the small one-eighth-size model of the
large aerodrome being launched from it into a sheet stretched in front of it to
act as a buffer. When it was found to work very satisfactorily, a large one,

twice this size, was immediately built for use with the steam-driven models Nos.
5 and 6.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 135

These models, Nos. 5 and 6, which had flown so successfully in 1896, had,
during the preceding twelve months, been completely overhauled and thoroughly
tested in preparing them for trials in actual flight. Many pendulum tests were
made on both aerodromes, and it was found after repeated trial that each could
be depended on to show a lift of sixty per cent of its flying weight.

This was more than sufficient for flight, but in order to insure successful
trials and avoid delay no aerodrome was launched until it had shown previously
its ability to generate enough power to maintain for at least two minutes a lift
of at least fifty per cent of the total flying weight.

Models Nos. 5 and 6, having thus proved their readiness for trial in flight,
were accordingly, in April, 1899, taken to Chopawamsiec Island, together with
the old ‘‘ overhead ’’ launching apparatus and the new one above described, and
placed on a small house-boat similar to the one which had been used in 1896.
Two men were detailed for this special work, and were first employed in mount-
ing the old launching apparatus for a few preliminary tests with it, in order to
make sure that the aerodromes were in proper working order before trying
them on the new ‘‘ underneath ’’ one. After considerable delay, due to various
causes, this apparatus and the aerodromes were got into proper working con-
dition, and during June, July and August the following flights were made with
these machines, the record being condensed from the reports made by the writer
to Mr. Langley while he was abroad.

ConpENSED ReEcorp or FrnicHts or Arropromes Nos. 5 anp 6 FROM

JunE 7 to Aucust 3, 1899
Lo A ~
JUNE 7—AERODROME NO. 6

After making a preliminary test of the engines and boiler, with the aero-
drome mounted on benches inside the house-boat, to insure that everything con-
nected with the power plant was in proper working order, the aerodrome was
mounted on the launching apparatus on top of the house, the various parts
were assembled and everything made ready for a flight. As it was calculated
that this aerodrome would require a soaring speed of something like twenty-five
feet a second, the springs which furnished the motive power for the initial ae-
celeration of the car were adjusted to the proper tension to cause it to reach a
speed of approximately twenty-three feet a second at the moment of launch-
ing. Everything being in readiness the burners were lighted but worked some-
what sluggishly at first, so that two minutes were consumed in raising a steam
pressure of 110 pounds. Although this pressure should have been reached within
one minute after lighting the burners, and the extra minute which had been
consumed had made a drain on the supply of fuel and water which should have

136 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

been left for consumption during flight, yet it was thought best to launch the
aerodrome, so at 12.37 p.m. the car was released and the aerodrome launched.
The launching apparatus worked perfectly; the aerodrome started off smoothly,
and immediately after being released from the car it dropped slightly and be-
gan to turn to the right. It had been impossible to move the house-boat out
into the stream so as to point the launching apparatus directly into the wind, as
one end had settled slightly on the muddy beach in consequence of the existing
low tide. For this reason it was necessary to launch the aerodrome due south,
while the wind, which was very light, was from the north-northeast, and, there-
fore, blowing on its port quarter. The effect of the aerodrome turning to the
right immediately after being launched was that it caused the wind to strike it
to an increasing extent on the port side until, finally, it was going directly with
the wind. It did not, however, continue in this direction, but kept turning to
the right in a circle until it headed directly into the wind, which, now striking
the under instead of the upper surface of the wings, immediately caused the
aerodrome to rise. It continued circling, making three complete circles of ap-
proximately 200 feet diameter, dropping slightly when moving with the wind, but
rising when moving against it, until, at the completion of the third circle, it
had altered its path to such an extent that the left front wing touched a tree and
caused the front of the machine to dip a little. It, however, kept up its flight,
but the contact with the tree had so lowered its bow, and apparently also caused
the wings to be twisted to such an extent, that it seemed unable to rise again,
and after making another quarter circle it descended. Although the propellers
were still turning when it struck the water, they had very greatly decreased
their speed, making it apparent that the power had been very greatly reduced
through the exhaustion of the fuel and water supply. The aerodrome did not
sink, but slowly drifted with the current of the creek and was recovered in about
five minutes and brought to the house-boat, where the wings were dismounted
and dried, and the metal parts were carefully wiped off to prevent them from
rusting. The path of this flight is plotted on a portion of a coast-survey chart
and is shown in Plate 33.

This erratic circling at first seemed unaccountable, but on closer examina-
tion, after the aerodrome had been brought into the house-boat, it was found
that the pin which connects the synchronizing gear to the port propeller shaft
had been sheared off. This had evidently happened while the aerodrome was
still on the launching apparatus. The effect of this was to throw the total work
of the water-cireulating pump on the starboard engine, thus giving the port en-
gine less work to do, and consequently making the port propeller run much
faster than the starboard one, and thereby causing the peculiar and erratic cir-
cling of the aerodrome. It is evident that the undulatory motion of the aero-

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 137

drome was due to the fact that, when it was moving against the wind, the speed
relative to the air was greater than when it circled so as to go with the wind, and
that this greater relative velocity increased the lifting power of the aerodrome.

The total time of the flight was 57 seconds, and the distance covered was be-
tween 2000 and 2500 feet, thus giving a speed of a little less than 30 miles an
hour. Cemparing this flight with that of November 28, 1896, made by the same
machine, it will be noted that in the earlier flight the velocity was practically
the same, but that the time of flight and the distance traversed then were nearly
twice as great as in the present case.

A complete record of the details, not only of weight, but also of the position
of the wings, the center of gravity, ete., which show the exact condition of the
aerodrome when it made this flight, will be found in the appendix (Data Sheet,

No. 3).
JUNE 13—AERODROME NO. 6

In the flight of June 7 there was a slight trembling of the aerodrome while
it was in the air, and although this was probably due to the fact that the syn-
chronizing gear was out of operation on account of the shearing off of one of
the pins which held it, allowing the port engine to run faster than the star-
board one, it was thought possible that some of the trembling might be due to

rhe)

the ‘‘ wind-vane ’’ rudder, which had been added to represent the equivalent of

a steering device by which the operator would control the direction of the

cé }

large machine. It was decided, therefore, to omit the ‘‘ wind-vane ’’ rudder in
the present test, but to test the aerodrome with the same equipment of single-
tier wings and Pénaud tail that had been used in the previous flight, the reel
and float being moved to bring the CG the same as on June 7.

Everything being in readiness, with the launching track pointed south, and
the wind blowing only about 54 miles an hour from the southwest, the burn-
ers were lighted and 63 seconds were consumed before the steam pressure rose
to 100 pounds. Although the valve which controlled the burner was open to its
full extent the pressure showed no tendency to rise above 100 pounds, which
was not considered quite high enough to furnish sufficient power for a success-
ful flight, but as it was desired to determine at once at how low a steam pressure
the aerodrome would fly successfully, it was decided to launch it even at this
pressure. The launching apparatus was accordingly released and the aerodrome
started off, gliding down about three feet immediately after being released, and
then rising again, turning slightly to the right and then heading directly for the
Virginia shore, where it seemed that it would smash itself in the heavy growth
of timber, but when it was about 250 feet from the shore it turned towards the
right and started back towards the island. The wind, however, which was

blowing from its rear, evidently got down the smoke-stack and put out the fire,

138 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

for the aerodrome commenced to descend as soon as it turned its back to the
wind, and came down in the channel of the creek. The path of this flight is
shown by the solid line in Plate 34.

The total distance covered, as measured by plotting the course of its flight on
the coast-survey chart, was about 1800 feet, and the length of time of flight was
40 seconds. The aerodrome was immediately recovered and brought into the
house-boat, where it was found that there were still about 1000 grammes of
water and 100 grammes of fuel unused in it, showing conclusively that the fire
had been put out by the wind.

Upon inspection it was found that the aerodrome was uninjured, and al-
though the burner had not worked at all satisfactorily, yet as the weather was
exceedingly favorable it was decided to make another trial with it immediately,
using the superposed wings.’

Everything being in readiness the burners were lighted, and 70 seconds
were consumed before the pressure rose to 90 pounds, beyond which it was-im-
possible to make it rise. Although it was felt certain that 90 pounds was not
sufficient pressure to furnish the power necessary, yet as a storm was approach-
ing in the distance, it was decided to launch the aerodrome, as it could at least
be determined whether it was properly balanced for the superposed wings.
When a total of 75 seconds had been consumed the car was released and the
aerodrome was launched. The wooden arrangement for pressing down on the
top of the wings to keep the aerodrome from being injured by the wind while
it was on the car had been raised to the proper height for the superposed
wings, but it had not been noticed that the sticks which support this arrange-
ment had been elevated so much that they would come in contact with the beam
extending across the boat, and from which the launching track was supported.
Just as these sticks reached the cross-beam, however, it was noticed that they
projected about three inches above the lower side of it; but the next moment
they struck it, and although the force with which the car was running broke all
four of them, the blow was sufficient to slow down the car, and thereby cause
the aerodrome to be launched at a very greatly reduced speed; not over one-
fifth of what it should have been. The shock of breaking these sticks evidently
jarred the burners so that the fire was extinguished, for the aerodrome shot
forward for about 25 feet and settled with everything intact, and with its mid-
rod perfectly horizontal. The aerodrome itself sustained absolutely no injury,
coming down as easily as though it had been lowered by a rope, and would
have been given another trial immediately but for the fact that it was very
late in the afternoon and darkness was rapidly approaching. The data on set-
ting of wings, tail, ete., are shown on Data Sheet No. 4 (Appendix).

*These wings are described in Chapter VI, pp. 191.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 139

JUNE 22——-AERODROME NO. 6

After several days’ delay, due to numerous small but exceedingly annoying
troubles,—such as the leaking of boilers because of defects in the copper tubing,
and the bursting of the air tank, due to its beimg pumped up to an excessive
pressure, which a defective pressure gauge had failed to indicate,—Aerodrome
No. 6 was made ready for another trial, and it was decided to test it again with
the superposed wings which had been used in the second experiment of June 13.
The aerodrome was mounted on the ‘‘ overhead ’’ launching apparatus, which
it will be remembered had been used in all the previous tests, and after 90 sec-
onds had been consumed in raising a steam pressure of 110 pounds, it was
launched directly into the wind, which was due south. After leaving the launch-
ing car, the aerodrome flew straight ahead for about 75 feet, when it suddenly
turned its bow up into the air at an angle of about 15 degrees, and it seemed
that the machine would be blown back onto the house-boat. However, when the
rear end of the tail was within about 10 feet of the boat, and only about 10 feet
above the water, it suddenly regained its equilibrium and went straight ahead
again in the face of the wind with the guy-posts only about 4 feet above the sur-
face of the water, flying almost exactly horizontally for a distance of about 100
feet, when the bow again suddenly became elevated. As the aerodrome was so
close to the water, the wind forced it down until the burners were extinguished
by coming in contact with the water. This brought the aerodrome to a stand-
still absolutely uninjured, the propellers being several inches above the water
when they quit turning. The aerodrome was brought into the house-boat and
thoroughly dried out, and another trial would have been made with it imme-
diately but the wind which had been steadily increasing was now blowing some-
thing more than 12 miles an hour, and it was considered best not to attempt ex-
periments in so strong and gusty a wind, for fear of the wings being broken
by the wind suddenly veering and striking them on the side or rear while the
aerodrome was still on the launching apparatus. The peculiar action of the
aerodrome in the air appeared to be due to the fact that the propellers inter-
fered more with the lifting power of the rear superposed wings, as they were
then constructed, than they did with the ‘ single-tier ’’ ones. The data on the
setting of the wings, tail, ete., are shown on Data Sheet No. 5 (Appendix).

Tt was also found after the experiment that one of the workmen, in assem-
bling the machine on the launching car, had secretly increased the stiffness of
the spring which controls the elasticity of the Pénaud tail. The effect of this
increase in the stiffness of the Pénaud tail might at first thought appear to be
similar to that of moving the center of pressure forward. Upon a closer analy-
sis, however, it will be seen that the effect is very much greater, as excessive
stiffness of the Pénaud tail not only causes the aerodrome to elevate its bow,

140 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

but requires the overcoming of a strong downward force at the rear, even more
serious than would be caused by placing an extra load at the rear of the ma-
chine without regard to its effect on the balancing. In experiments of this
kind, however, the workmen get certain ideas of their own as to how the work
should be conducted, and it is almost impossible in assembling the aerodrome to
prevent them from making adjustments which are quite different from those
which they have been directed to make, and which have been definitely planned
with a view to determining the effect of slight changes which it is desired shall
not be masked by changes of any kind in other details.

99

JUNE 23—-AERODROME NO. 6

The wind, which had been blowing half a gale all day, gradually quieted
down towards sunset and at five o’clock was very light, blowing only two miles
an hour from the east-southeast. As one of the rear superposed wings had been
injured on the previous day in carrying the aerodrome into the house-boat after
its short and erratie flight, it was decided to use the ‘‘ single-tier ’? wings in
this experiment, and also to continue using the ‘‘ overhead ’’ launching appa-
‘atus for a few more flights. Everything being in readiness, the burners were
lighted and 70 seconds were consumed in raising a steam pressure of 120 pounds,
at which pressure the aerodrome was launched. It started straight ahead, drop-
ping not more than a foot, and flying on an absolutely even keel for about 800
feet, when it suddenly turned to the left and made a short half circle of about
100 feet diameter, heading for a point about 150 feet east of the house-boat.
When it was about 200 feet from the shore, a sudden gust of wind caught under
the Pénaud tail, raising the rear portion of the aerodrome and causing the bow
to point down at an angle of about 30 degrees. The aerodrome kept this angle
and struck the shallow water only about 20 feet from the shore. The aerodrome
was comparatively uninjured, and another flight would have been made imme-
diately but for the fact that by the time the aerodrome had been properly in-
spected it was quite late, and entirely too dark, and there would have been dan-
ger of losing it in the adjacent marshes, which are difficult to traverse even un-
der the best conditions of tide and light. The path of this flight is shown by the
dotted line in Plate

JUNE 27—AERODROME NO. 9

While the preceding tests had been going on with Aerodrome No. 6, such
time as could be spared for it was spent in getting Aerodrome No. 5 into proper
condition. The copper tubing from which the boilers for both aerodromes were
made was greatly inferior to that which had been used in previous years, and
as this tubing could be procured only by having it specially drawn to order in
France, and as it required several months after placing an order before the tub-

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PATHS OF FLIGHT OF AERODROME NO. 6, JUNE 13 AND 23,

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 14]

ing could be delivered, it was necessary to make the best of what was already on
hand. The copper tubing for the boilers which had been used in 1896, after be-
ing carefully annealed and filled with fine sand, could be wound into a perfectly
smooth helix, free from all wrinkles, indentations, and so forth, on the inner
side of the coil. But no amount of care, both in annealing and in winding this
present lot of tubing, would produce a smooth helix, the tubing being badly
wrinkled on the inner side of the coil in spite of every precaution. These
wrinkles, however, were not so much the cause of serious trouble as was the
fact that the tubing was not uniform in quality, each length of it having nu-
merous rotten spots which did not always show up in the winding, but which
gave way after the boiler had been completed and one or two preliminary runs
in the shop had been made with it. While the effect of such small things can-
not be appreciated from merely reading about them, yet they were the cause
of the most exasperating annoyance and delay, as no sooner had the aero-
drome been gotten into what appeared to be perfect working order than the boiler
would break at one or more points, thus causing a delay which at the moment
would seem to involve not more than a few hours, but before everything was
again in working order would amount to several days.

However, after much perseverance, Aerodrome No. 5 was put in satisfac-
tory working condition, and on June 27 was launched with its ‘‘ single-tier ”’
wings and Pénaud tail. The data on settings of wings, tail, ete., are given on
Data Sheet No. 6. After lighting the burners, 70 seconds were consumed in
raising a steam pressure of 120 pounds Immediately upon leaving the launch-
ing car the aerodrome started to rise with its bow elevated to an angle of about
15 degrees. It flew straight ahead about 80 feet, when it came backward and
downward and touched the water about 40 feet from the boat. The failure of the
aerodrome to fly properly was evidently due to its not being in proper balance.
The cause of this lack of proper balance was not immediately apparent, but was
very soon detected and will be discussed later on.

JUNE 30—AERODROME NO. 5

After several days of incessant rain and strong winds, which prevented an
experiment, the weather became brighter and the wind quieted down and the
afternoon of June 30 was almost ideal for an experiment. At five o’clock Aero-
drome No. 5, with ‘‘ single-tier ’’ wings and Pénaud tail, was placed on the
launching apparatus, a few minutes later the burners were lighted, and just as
the propellers started to turn a racking noise was heard. Upon investigation
it was found that the circulating pump had broken. The break was a very small
matter and could have been repaired in an hour, but it was then too late to re-
pair the damage and get a flight before dark, so the aerodrome was reluctantly
dismounted and the men put to work repairing the broken pump.

142 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

suLY 1 To suLyY 8

The great disadvantage of conducting the experiments at a point forty
miles from the city and the shops was felt at all times. Workmen, even of the
very best class, cannot be kept contentedly at work at a point so far removed
from their homes, even by bringing them to the city on Saturday afternoon and
carrying them back to the experimental grounds the following Monday. More-
over, it is worse than useless to try to get even as much as one-third the ordi-
nary amount of work done if there is the slightest excuse for tightening anchor
ropes, watching passing boats, or wasting time on any of the multitudinous small
variations from their usual routine of life.

On July 7, Aerodrome No. 5, equipped with ‘‘ single-tier ’? wings and Pé-
naud tail, was made ready for a flight in the afternoon. The settings of the
wings, tail, ete., are given on Data Sheet 6. Using the ‘‘ overhead ’’ launching
apparatus, the aerodrome was launched with a steam pressure of 115 pounds.
Immediately upon being launched its bow rose to an angle of about fifteen de-
grees or more, and the aerodrome came backward and downward and touched
the water about three or four feet from the house-boat.

It may be well to recall from what has been said in Part I, Chapter IX, that
Aerodrome No. 5 is the one with the very low thrust line, and in 1896 had its
‘* separator ’’ several centimetres in front of its center of gravity. When this
aerodrome was overhauled just previous to these experiments, the separator
was moved back to the same relative position as that in Aerodrome No. 6, so that
the gradual depletion of the water supply during flight would not cause it to be-
come light in front of the center of gravity.

In the launching of Aerodrome No. 5, above described, it showed no ten-
dency to drop immediately upon leaving the launching ways, but on the con-
trary its bow in every case rose almost immediately until it was at an angle of
about fifteen degrees or more. From the photograph (Plate 35) it will be no-
ticed that the wings of the aerodrome are held down by the longitudinal strips,
A, fastened to cross-beams attached to the launching ear. If, now, the launch-
ing speed is too great and the aerodrome tries to rise immediately upon being
released, the front end, which passes from under the launching car before the
rear does, and is thus free to rise, will immediately rise, while the rear cannot
rise until it has passed entirely in front of the ear, which being a distance of
several feet requires an appreciable fraction of a second, during which time the
bow of the machine has been able to rise to quite a steep angle. This has the
effect of slowing down the aerodrome so that it does not get quite the proper
chance to start on its flight with a minimum head resistance.

In view of the above facts. it was decided to decrease the speed of the
launching car slightly when using Aerodrome No. 5, so that this matter could
be thoroughly tested out.

SAVM-DNIHONNV1 NO S ‘ON AWONGONSY

menemmeeeee | -Jaee | ee - ee 1 ee 4 oes | +), es _— . SIOMATWAAONY OF SNOLINAININOY NVINOCHUTIWS

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 143

guLy 11 vo suLY 14—akERODROME NO. 9

The very early morning preceding actual sunrise on July 11 was undoubt-
edly as calm as it is possible to find; there was absolutely no breeze stirring
and the water in the river was as smooth as glass as far as one could see. The
anemometer cups were stationary, the wind vane stood absolutely parallel to
the launching apparatus and everything promised a most successful experiment.
After mounting the aerodrome on the ‘“ overhead ’’ launching apparatus the
burner was lighted, and while the steam pressure was still rising and the pro-
pellers were revolving faster and faster all the time, there was a snap and they
ceased to turn. The fire, which was burning fiercely, ran the pressure imme-
diately to 150 pounds. An attempt was at once made to start the propellers
again by giving them an initial turn by hand, it being thought possible that a
sudden gush of water had taken place and, accumulating m one end of the en-
gine cylinder, had blocked the engine. However, as the engine refused to keep
the propellers going after they were started, and as the pressure was still rising
very rapidly, the burner was shut off and an investigation made. Upon remoy-
ing the hull covering, it was found that the connecting rod bearing had broken
off short near the crank pin of the engine, and that it would be necessary to
take the part to Washington in order to repair it, as there were no machine
tools on the house-boat.

After several days of exceedingly bad weather, the conditions grew more
favorable. Late in the afternoon of July 14, Aerodrome No. 5 was again placed
on the “‘ overhead ”’ launching apparatus and prepared for a trial. After light-
ing the burners, 95 seconds were required to raise a steam pressure of 120 pounds.
Upon leaving the launching apparatus the aerodrome went directly ahead for
a few feet, but immediately commenced to rise, elevating its bow to an angle of
20 degrees by the time it had travelled 40 feet. With its bow in this position,
it was blown back towards the house-boat and a little to the right of it, and,
when within about 5 feet of the water, suddenly righted itself and started ahead
again, rising all the time and reaching a height of about 20 feet by the time it
had travelled 100 feet. In the meantime the bow had again become elevated to
an angle of about 15 degrees and the aerodrome was blown backwards and down-
wards again. Just before reaching the water it started to right itself, but it
had descended so that the front guy-post was in the water, thus destroying its
equilibrium and causing it to settle into the water. The path of this flight is
shown by the peculiar S-shaped line in Plate 54.

In the adjustments preliminary to the above trial the Pénaud tail was ele-
vated to an angle of 74 degrees when the aerodrome was stationary in the shop.
This excessive elevation, coupled with the fact that the center of gravity was
also probably a little too far forward, no doubt accounts for the erratic flight.
The data on setting of wings, tail, etc., are given on Data Sheet No. 7 (Appendix).

144 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

JULY 19—aERODROME NO. 9

After several days of exceedingly bad weather the conditions were more fa-
vorable on July 19. Since the last experiment on July 14 the coefficient of elas-
ticity of the Pénaud tail had been decreased, the rear wings moved back 5 centi-
metres, and the ‘‘ float?’ so placed that the center of gravity of the machine
was brought to the same position it had had on that day, that is, 2 centimetres
back of the line of thrust. With this arrangement, assuming that the CP is
over the CG, we should have an apparent efficiency of the rear wings of 63.6 per
cent, since the distance between CP» and CG is 79.7 centimetres, and the dis-
tance between CP,» and CG is 125.3 centimetres. With the adjustment of July
14, the distance between CP)» and CG was 79.7 centimetres, and the distance he-
tween CP,» and CG was 118.3 centimetres, thus allowing for an apparent effi-
ciency of 67.37 per cent for the rear wings. It will be recalled that in the un-
successful flight of July 14 the midrod of the aerodrome was inclined at an angle
of about 20 degrees during most of the time that it was in the air, thus indi-
cating that the front wings were lifting proportionately more than they should.
On July 14 the Pénand tail had a negative elevation of 7° 30’, and it required
1240 grammes placed at its center to bring it to the horizontal. On July 19 the
elevation of the tail was changed to 5° and a weaker spring for controlling the
elasticity was substituted, so that it required only 200 grammes placed at the
center of the tail to bring it to the horizontal. A rubber band, of about one-
half the strength of the upper spring, was attached by means of a cord to the
lower guy-post and the lower vertical ribs of the tail, so that the tail would be
elastic both ways. This rubber band was in place and acting to help draw the
tail down when the above measurement of the coefficient of elasticity was made.
A rubber band connected to the lower side of the tail was also used in the
flight of July 14, but it was so very weak, compared to the upper spring, that its
effect was negligible.

The effect of this change in the balancing of the aerodrome, and also the
more considerable effect which the coefficient of elasticity of the tail has on the
balancing, will be immediately noticed from the description of the next flight.
The data on setting of wings, tail, ete. are given on Data Sheet No. 8.

At 3 p.m., the wind having died down, Aerodrome No. 5, equipped with its
‘« single-tier ’’ wings and Pénaud tail adjusted as above, was placed on the
‘ overhead ’? Jaunching apparatus. After lighting the burners, one minute and
thirty seconds were required to raise a steam pressure of 120 pounds. Imme-
diately upon leaving the launching apparatus, the aerodrome started straight
ahead, dropping about 3 feet by the time it had gone 100 feet; it then rose
with its midrod at an angle of about 6 or 8 degrees, regaining its level very
quickly, however, and making three of these undulations by the time it had gone

rt

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 145

300 feet. It continued straight ahead for another 300 feet and began to circle
to the left, the diameter of the first circle being about 200 feet. As soon as it
started to cirele, it rose with its midrod at an angle of about 15 degrees, and
by the time it had made its first half turn it started to descend, coming down to
within 15 feet of the water. As soon, however, as it had completed this first
turn, it again rose, making another half circle, then, upon the completion of
this half turn of the second circle, descended, this time to within 10 feet of the
water, rising again for the third half turn, but again descending to within 2 feet
of the water at the completion of this third circle, and then rising and complet-
ing the first half turn of the fourth circle. By this time, however, it had sunk
so near to the water that the guy-posts caught in the tall grass while it was de-
seending just before the completion of the fourth circle, thus pulling the aero-
drome down into the water with the propellers still running. The total time
the aerodrome was in the air was 46 seconds. The total number of revolutions
of the propellers was 488, or at the mean rate of 637 R. P.M. Upon examining
the aerodrome, after it was recovered, it was found that there were 925 erammes
of water left in the separator, the fire having been put out by the aerodrome
coming down into the water.

When the aerodrome first commenced to circle during its flight, it was no-
ticed that the front wing clamps had twisted on the midrod, the left wing being
dipped downwards, and the right one, of course, being elevated, and the peculiar
circling of the aerodrome was undoubtedly due to this facet. The cause of the
wing clamp twisting on the midrod was that one of the workmen forgot to
tighten one of the screws of the wing clamp when the wings were being adjusted
on the aerodrome. But for this unfortunate twisting of the wings, it is probable
that the flight would have been perfectly straight and the distance covered would
have been considerably greater than it was, the total path traversed being about
2600 to 2800 feet, found by plotting the path on the coast-survey chart and meas-
uring it.

JULY 27—aPRODROME No. 6

As the proper balancing of both Aerodrome No. 5 and No. 6 had now been
determined with reasonable accuracy, and as much more time had already been
given to the experiments than had been intended, it was decided to dismount
the ‘‘ overhead ’’ launching apparatus at once and substitute the ‘‘ underneath ”’
one, so that it could be immediately determined whether this newer plan for
launching the aerodrome by a car supporting it from underneath would be suit-
able for use with the large machine. After a considerable period of exceedingly
bad weather, during which time the change was made in the launching appa-
ratus, the weather conditions became more favorable on July 27. Aerodrome
No. 6, equipped with ‘‘ single-tier ’’ wings and Pénaud tail, was mounted on the

14

146 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

‘* underneath ’’ launching apparatus, and everything was got ready for a flight.
On lighting the burners, they failed to work properly, and, upon investigation,
it was found that the air valve controlling the air pressure on the gasoline
tank, was out of order. While this was being repaired, the wind rapidly in-
creased in velocity and became very gusty, thus endangering the aerodrome, as
the wings were very liable to be broken by the wind suddenly veering more rap-
idly than the house-boat could turn or the turn-table could be moved, and thus
striking the wings from the side and putting an enormous upward pressure on
them, owing to the fact that the diedral angle between them gave to each wing
an elevation of 7§ degrees from the horizontal. The aerodrome was accord-
ingly dismounted and everything kept in readiness for a trial, with the hope
that the wind would die down, or at least become steady, but it did not do so
until after dark.

JULY 28—aBRODROME NO. 6

Aerodrome No. 6, equipped with ‘‘ single-tier ’’ wings and Pénaud tail, was
launched from the ‘‘ underneath ’’ launching apparatus. There was a dead
calm, the river not showing a ripple; the wind vane pointed to the northeast,
but as the tide was low and the boat was aground, the launching track was point-
ing due south. At 7 a.m. the burners were lighted, and 80 seconds were con-
sumed in raising a steam pressure of 120 pounds. Everything worked perfeetly ;
the uprights on the car, which initially support the aerodrome and upon its be-
ing released are instantaneously pulled down by rubber springs, as well as the
disappearing part of the track, acted without the slightest hitch. Immediately
upon leaving the launching apparatus, the aerodrome depressed its bow to an
angle of between 3 and 4 degrees and made a direct line for the water. At
this angle it struck just on the opposite side of the channel, about 300 feet from
the house-boat, and while several minor parts, such as guy-posts, were injured
no damage of importance was done. Owing to the difficulty of getting through
the marsh and recovering Aerodrome No. 6, it was found impossible to make
another trial with No. 5 before the wind had increased to a prohibitive veloc-
ity. The path of this flight is shown by the dotted line in Plate 36. The data
on setting of wings, tail, ete., are given on Data Sheet No. 9.

The last previous trial of Aerodrome No. 6 was made on June 23, and the
balancing at that time was evidently correct for the settings of the tail which
were then used. The Pénaud tail then had an elevation of 74 degrees, and the
coefficient of elasticity was such that 1240 grammes were required at the center
of the tail to deflect it to the horizontal. In the trial above recorded, on July
28, the adjustments of the wings were practically what they were on June 23,
the CG being moved forward 1 centimetre, but the Pénaud tail had an elevation
of something less than 5 degrees, and the coefficient of elasticity was such that

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 147
200 grammes placed at the center were required to deflect the tail to a horizontal.
It was not intended that the angle of the tail should have been less than 5 de
grees, but it was found that one of the workmen had improperly attached the
fastening wire, and had considerably decreased the angle. This last adjustment
of the Pénaud tail should have been the same as that used on Aerodrome No.
5 in its flight of July 19. The CG had purposely been moved forward slightly,
but the effect of moving the CG forward and at the same time decreasing the stiff-
ness and angle of the tail was shown by this flight.

The above trial not only very clearly emphasizes the importance of ecare-
fully determining what the elasticity of the Pénand tail should be, but also em-
phasizes the fact that even the best workmen, who have had several years of
experience, cannot be relied on in anything which requires that everything be
done exactly right and not nearly right.

JULY 29—AaERODROME NO. 5D

The aerodrome equipped with ‘‘ single-tier ’? wings and Pénaud tail was
launched from the ‘‘ underneath ’’ launching apparatus at 9 a.m., 1 minute and
30 seconds having been required to raise 120 pounds steam pressure. The wind
was from the southeast, with a velocity of 3 miles an hour, and the launching
track was pointed directly into it.

The launching apparatus, with the disappearing track, worked perfectly,
and the aerodrome started straight ahead, dropping slightly at first, but imme-
diately regaining its level and going ahead, gradually raising its bow to an
angle of about 8 or 10 degrees, and slightly slacking up its speed by the time it
had gone about 300 feet. It then made a circle to the left of a radius of about
75 feet and started back. As soon as it had made this turn it regained its level
and directly regained its speed. But as soon as it had speeded up again it ele-
vated its bow, which slackened its speed as before. It then again righted itself,
still going in the same direction and crossing the sand-bar on the point of the
island at a height of about 40 feet. As soon as it had crossed the sand-bar, it
again made a circle to the left with a radius of about 75 feet, heading directly
for the house-boat, but when it had got back above the sand-bar it again circled
to the left, passing directly between two tall trees, and barely missing them,
and still circling to the left, when it again reached the opposite side of the sand-
bar. It, however, kept on circling to the left and once more started back to-
wards the house-boat, this time passing to the left of the trees and again barely
missing them, and completing this, its second, circle over the sand-bar. It then
started due north, heading directly for Quantico, but by this time something
had evidently happened to the burners as the fire went out, and the propellers
gradually slowed up. However, it kept on towards Quantico, gradually de-
scending on an even keel, and came down in the water at a point about 500 feet

148 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 2

from the sand-bar and about 1000 feet from the house-boat. The propellers
had almost ceased turning when the aerodrome came down into the water, and
it settled almost as quietly as though it had been picked up and placed there,
so that no damage was done to it.

The total time that the aerodrome was in the air was 63 seconds, and the
total length of flight was about 2500 feet. The path of this flight is shown by
the dotted line with the double circle in Plate 36. The data on settings of wings,
tail, ete., are given on Data Sheet No. 10.

As soon as the workmen had had their breakfast, Aerodrome No. 5 was
again placed on the launching apparatus, equipped this time with the super-
posed wings and Pénaud tail. Upon lighting the burners, it was found that they
did not work properly, a small piece of soot having clogged up the tip of the
aporizing coil. While this trouble with the burners was being remedied, the
wind increased to such an extent that it was found necessary to remove the
aerodrome from the launching apparatus to prevent its being injured by side
eusts. As it was Saturday and the wind showed no signs of quieting down,
the experiments were discontinued until the next week.

AUGUST 1—AERODROME NO. 5

After placing the aerodrome on the launching apparatus and getting every-
thing in readiness for a flight, upon lighting the burners a sudden sheet of
flame shot out of the smoke-stack and so seriously charred three panels of each
of the rear wings that they had to be removed for repairs. The silk covering
of the wings had been coated with a special fire-proofing preparation, but the
intensely hot flame, of course, charred all the silk that it came in contact with.

By the time that the wings had been repaired, and the defect in the burner
which caused the accident had been remedied, a severe storm had arisen, mak-
ing it necessary to remove everything to the interior of the boat. While wait-
ing for the weather to become more suitable, a test of the engine of Aerodrome
No. 5 was made inside of the house-boat. In this test a steam pressure of 140
pounds was obtained, giving 650 R. P. M. of the round-end, 100-centimetre pro-
pellers, which previous tests had shown to mean a thrust of 7480 grammes.
As the flying weight of the aerodrome was now 14,104 grammes, the thrust ob-
tained would correspond to a lift of 53 per cent of the flying weight, which
was maintained in this test for 90 seconds.

As the CG of Aerodrome No. 5 seemed to be a little too far forward in the
flight of July 28, it was decided to change it slightly, and it was moved back 4
millimetres.

A trial run in the house-boat was also made on Aerodrome No. 6, while
waiting for the weather to become more suitable, but, unfortunately, the result
of this test was disastrous. The aerodrome had been placed on trestles and

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PATHS OF FLIGHT OF AERODROME NO. 5, JULY 29, 1899

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 149

held down to the floor by wires fastened to the cross-frame. In the midst of
the test one of the wires slipped, allowing the aerodrome to push forward and
thus permitting the propellers to come in contact with the wires which held
it to the floor. Both propellers were entirely demolished and the cross-frame
was broken off short just at the right-hand engine. The disaster was entirely
due to the carelessness of one of the workmen in tightening one of these wires,
a further example of the extreme heedlessness of workmen, even in the most
important details, which concern the very existence of the machine.

AUGUST 3—AERODROME NO. 5D

After the very satisfactory trial of Aerodrome No. 5 in the shop two days
previous, it was hoped, now that the weather had become suitable, that a good
flight with the superposed wings would be obtained. The aerodrome, equipped
with these wings, was accordingly placed on the launching apparatus and the
burners were lighted, but they refused to work properly, a steam pressure of only
80 pounds being obtained. After much delay the burners were finally got to
work properly, but the wind had increased in velocity to such an extent that it
was necessary to remove the aerodrome to the interior of the house-boat. As
the wind continued to increase in velocity it was decided to make another trial
of the aerodrome inside of the house-boat. Upon doing this it was very soon
found that there was a small! leak in the front turn of one of the coils of the
boiler, and the steam from this played directly against the burner, causing it to
work intermittently. A new coil was substituted, and after some adjustment a
very excellent run was obtained, the steam pressure reaching 130 pounds and
the propellers making 654 R. P. M.

In the afternoon the wind quieted down and the aerodrome, equipped with
superposed wings, was again placed on the launching apparatus. The burners
were lighted but again refused to work properly, the vaporizing tip beimg
stopped up with soot. This caused the burner to ‘‘ flood,’’ which sent a sheet
of flame through the stack and burned the rear right wing.

A new wing was substituted, the burner tip was cleaned out and everything
was again put in readiness for a flight. Upon lighting the burners, 1 minute and
58 seconds were required to raise 120 pounds steam pressure. The underneath
launching apparatus, with the disappearing track, worked perfectly, the aero-
drome dropping slightly, but going straight ahead. It, however, continued to de-
scend for a distance of about 100 feet, the bow being elevated about 5 degrees.
The bow then became horizontal, the aerodrome rising slightly at the same time,
but going only about 50 feet farther, when it again started to descend slightly,
and finally settled gently on the water between 300 and 500 feet from the house-
boat, with its bow elevated about 3 degrees. There was a hiss as the hull
touched the water, showing that the fire was still burning and making it im-

150 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 2

probable that the failure of the flight was due to lack of power. The data on
settings of wings, tail, etc., are given on Data Sheet No. 11.

The speed of the launching car, one foot in front of the point at which
the aerodrome was released, was twenty feet a second, as shown by the carbon
record sheet carried by the launching car and moved in front of a tuning fork
which had been set in vibration.

The aerodrome, being uninjured in the previous flight, was again placed on
the ‘‘ underneath ’’ launching apparatus, and before attaching the wings a short
run was made in order to see that everything was in proper working condition.
As everything seemed to be all right, the wings and tail were immediately ad-
justed for another trial. As the bow was slightly elevated in the previous trial,
it was thought best to bring the CG@ a little farther forward, and this was ac-
cordingly done. As the aerodrome also seemed to drop slightly in leaving the
launching car in the above trial, the tension of the launching springs was slightly
increased so as to increase the velocity at the moment of release.

Just as the sun was setting the aerodrome was again launched, 1 minute and
30 seconds having been required to raise 120 pounds steam pressure, but the
pressure was rising very rapidly at the moment of launching. There was an
absolutely dead calm prevailing, the river being as smooth as glass. The launch-
ing apparatus, with the disappearing track, worked perfectly. Immediately
upon being released the aerodrome went straight ahead, with its midrod hori-
zontal, but gradually glided downward as though the wings had very little lift-
ing power, and settled in the water about 200 feet from the house-boat. The ve-
locity of the launching car, 1 foot before the aerodrome was released, was 22
feet a second, as shown by the carbon record sheet.

In the above trials of the superposed wings, the conditions of the wind and
of the aerodrome were certainly as favorable as could be expected. There was
as much power being furnished by the engine as had been furnished in the pre-
vious flights with the ‘‘ single-tier ’? wings, and the balancing of the aerodrome
was exceedingly good. The superposed wings, unquestionably, had a fair trial
and proved inferior to the ‘‘ single-tier ’’ ones, for they had a supporting sur-
face of 2.75 square feet to the pound, whereas with the ‘‘ single-tier ’’ wings
there was approximately 2 square feet to the pound. The decreased lifting
power of the superposed wings seems to be another confirmation of the results
of the Allegheny experiments with the ‘‘ plane-dropper.’? ?

As more time had already been given to these tests than it seemed well to

2See “Experiments in Aerodynamics.” It will be recalled that in the experiments with the
“plane-dropper” there was a greatly reduced lifting power with superposed planes when their dis-
tance apart was one-half the width of the planes, unless a speed of about 42.5 feet a second was ob-
tained. In the above tests with the superposed wings, the speed was only from twenty to twenty-
two feet a second at the time of launching, and as the distance between the surfaces was only one-

half as great as their width, it is not surprising that the lifting power should not be as great as with
the “single-tier” wings.

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 151

spend on them at that time, owing to the pressure of the work of construction
for the large machine, it was deemed best to discontinue them for the time be-
ing, and as soon as time could be found for it, to construct a set of wings with
superposed surfaces, using only two surfaces and making their distance apart at
least equal to or greater than their width.

It will be remembered that the prime object in making these tests was to
obtain data for use in the balancing of the large aerodrome and in construet-
ing a launching apparatus for it. The chief deductions drawn from them were:
First: That it would be best to construct the first set of wines for the large ma-
chine on the ‘‘ single-tier ’’ plan, and later to make a set of superposed ones,
should further experiments with new designs develop a type of superposed sur-
faces which gave as good lifting power as the ‘‘ single-tier ’?’? ones. Second:
That the proportioning of the coefficient of elasticity of the Pénand tail should
be given as careful attention as the setting of the wings. Third: That the ‘‘ un-
derneath ’’ launching apparatus was equally as good as the ‘‘ overhead ’’ one,
and that both worked as well as could be desired; and, fourth, that while short
periods of calm weather might be expected during some part of the day on a
portion of the days of each month, yet the most favorable conditions were more
apt to be met with between the first break of day and the actual rising of the
sun, or from an hour preceding sunset until darkness actually came.

Tt will be noted that while considerable delay was experienced in making
these tests, nearly all of it was due to the very delicate adjustments required
in the power-generating apparatus of the aerodrome, but it should also be noted
that when these adjustments were accurately made the models operated exceed-
ingly well, and could be depended upon to give good flights of sufficient duration
to permit a careful study of their action while in the air.

In the experiments of June 27 and July 7, above described, the aerodrome
immediately after leaving the launching apparatus began to rise with its mid-
rod pointed upward at an angle of about 15 degrees. From Data Sheet No. 6,
which gives in detail the important data as to the settings of the wings, the
elasticity of the Pénaud tail,’ ete., we note that the tail had a negative angle of
74 degrees, and that the spring which held it at this angle was of such a stiff-
ness that it required 1240 grammes placed at its center of figure to depress it to
the horizontal. It will also be noticed that the position of the front and rear

5In fact the setting of the tail at a negative angle and fastening it to the frame by an elastic
or spring connection was only begun in 1896, and while it proved to be the key to the solution of the
problem of automatic longitudinal stability, yet it was not at that time so recognized, although the
first real test of the aerodromes after the elastic connection and negative angle of the tail were
adopted resulted in the epoch-making flight of No. 5 on May 6. By comparing the angle of the
tail on No. 5 in Plate 27A, Part I, with the angle of the tail on No. 6 in Plate 27B, Part I, it will be seen
that while the first had an angle of much less than 5 degrees, the latter had an angle of about 15
degrees. But the wooden springs changed so that it was not accurately known what the angle
really was at the time of either flight in 1896.

152 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

wings relative to the center of gravity of the machine was not the same as that
which existed at the time of the very successful flights of 1896, as shown by Data
Sheet No. 1 of No. 5, May 6, 1896. When the elasticity of the tail was adjusted
before making this test it was thought that it was made the same as in the ex-
periments of 1896, though accurate data as to the exact amount of this elastic-
ity had, unfortunately, not been kept.

A slight change had also been made in the method employed of attaching
the Pénaud tail to the machine. In 1896 the tail was attached to the machine
by means of a flat piece of wood (hickory) which had been steamed and bent to
the proper extent to cause the rudder to have a negative angle of about 5 de-
grees, but no accurate note was made of its angle or stiffness, so that in 1899
no data were available as to exactly what the angle had been or how stiff the
spring was. Owing to the fact that wood not only warps and twists, but also
that any piece which has been steamed and bent gradually loses a certain amount
of its curvature, it was decided in 1898 to change this method of attaching the
tail, the wooden spring being replaced by a coiled steel spring attached to an
upper guy-post and connected to the tail by a bridle wire fastened to the cen-
ter of figure of the tail.

After the experiment of July 7, 1899, a lower spring, consisting of small
rubber bands, was connected by a wire to the lower part of the rudder and
fastened to the guy-post, thereby more nearly reproducing the conditions ob-
tained when using a wooden spring, which, of course, tends to return the rudder
to its normal position when it is displaced in either direction. After attaching
this lower spring to the rudder, the experiment of July 14 was made, and it
was found that the aerodrome still flew with its midrod pointed upward at a
very steep angle. It was, therefore, felt certain that the upper spring on the
rudder was too stiff, and that it should not require so much as 1240 grammes
to bring it to the horizontal. This spring was, therefore, replaced by a weaker
one, and the angle of the rudder was also decreased until it had a negative angle
of only 5 degrees and required only 200 grammes placed at its center of figure
to bring it to the horizontal. From the description of the flight of July 19, it
will be seen that these changes immediately corrected the tendency of the aero-
drome to point its nose upward at such a sharp angle, and it will be later seen
that after a further slight adjustment the flight of July 29 was made, in which
the proper balancing was obtained and the aerodrome made a good horizontal
flight.

After these preliminary tests with the ‘‘ overhead ’’ launching apparatus,
it was dismounted and the ‘‘ underneath ’’ one substituted and the experiments
of July 28, 29 and August 3 were made. Everything connected with this ‘‘ under-
neath ’? launching apparatus worked perfectly from the start and four flights

of the aerodromes were made using it.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

EXPERIMENTAL FORMS OF SUPERPOSED SURFACES, 1898, 1899

(SEE ALSO PLATES 64 AND 65)

VOL. 27, NO. 3, PL. 37

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 153

Tt will be recalled that in ‘‘ Experiments in Aerodynamics ’’ Mr. Langley
made tests of the soaring speed, ete., of surfaces when superposed. In many
of his experiments with rubber-driven models, he also employed superposed sur-
faces. During the summer of 1898 several forms of superposed surfaces, of
a proper size for use on the steam-driven models Nos. 5 and 6, were con-
structed and were tested under as nearly as possible the same conditions as
would exist when used on the aerodrome, by mounting the surfaces on the whirl
‘ing-table and measuring their soaring speed, lift, drift, ete., to determine just
what arrangement of surfaces gave the greatest lifting effect with the least
resistance. Two of the forms which were tested are shown in Plate 37, Figs.
1 and 2, and Plates 64 and 65. At the conclusion of these tests, it was decided to
construct a set of surfaces on the plan shown in Plates 64 and 65, and to have
them ready for use on either of the models Nos. 5 and 6. These surfaces were
taken to Chopawamsiec Island in April, 1899, when all of the other aerodromic
material was first carried there. It was planned to make some tests with them
to determine whether or not it would be best to use superposed surfaces on the
large aerodrome or to follow the plan of ‘‘ single-tier ’’ ones, which had the
great advantage of having already proved their worth in the successful flights
of the models. On August 3, Aerodrome No. 5, equipped with these superposed
surfaces, was launched. It will be noted from Data Sheet No. 11 that the super-
ficial area of the superposed surfaces was considerably greater than that provided
by the ‘‘ single-tier ’’ ones, and on the assumption of the same efficiency per unit of
surface in both cases, the aerodrome should have soared at a less speed and re-
quired less power when using the superposed surfaces. The results obtained,
however, were just the reverse, the aerodrome being unable to sustain itself when

?? ones it was evi-

using the superposed surfaces, whereas with the ‘‘ single-tier
dent that a slight excess weight might easily have been carried without preventing
the aerodrome from soaring’ properly.’ While it was felt that these tests were not
entirely conclusive as to the superior lifting power of the ‘‘ single-tier ’’ sur-
faces, yet as the engine builder was constantly promising, each time with in-
creased emphasis, that he would within less than a fortnight deliver the engine
for the large aerodrome, and that it would develop even more power than the
specifications called for, it was deemed best to cease the experiments with the

models and concentrate all effort on the completion of the large aerodrome

‘ ””

frame and the construction of a set of ‘‘ single-tier ’’ supporting surfaces for

”” supporting surfaces

it. It was recognized from the first that the ‘‘ single-tier
lacked the rigidity which could be secured by the truss construction afforded by
the superposed plan, yet these models, which were the only machines in the
history of the world that had ever flown successfully, had been equipped with

“« single-tier ’’ surfaces; and the experience so dearly bought during the long

154 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

years of development of these models had taught the very valuable lesson that
in work of this kind where we have no margin on anything, but everything has
to be calculated on the ‘‘ knife-edge ”’ basis, it is an exceedingly unwise thing to
introduce any modification from what has been proved to be satisfactory, unless
such modification is absolutely necessary.

The principal object in building the one-eighth size model of the large aero-
drome, as mentioned in the first part of this chapter, was to determine by act-
ual experiment whether the new form of ‘‘ underneath ’’ launching apparatus,
which had just been designed, was likely to prove as satisfactory as the original
“overhead ’’ type, which had been used in the successful flights of the models in
1896. Yet after it was completed this aerodrome was found so very strong and
stiff, even though roughly constructed by merely tying the joints of the tubing
together with wires and soldering over the joints, that it was decided to equip
it with power, if a suitable form of power could be found which could be easily
applied. Just at this time liquid air as a motive power was attracting consid-
erable attention all over the country, and attempts were made to procure a
small power plant for operation by liquid air. After devoting considerable time
to the matter it was found impossible to do anything with it just at that time, as
the liquified air could not be obtained in Washington, and one of the chief ex-
perimenters in New York, who had been given a commission to make certain ex-
periments at his plant, so continuously delayed beginning them that it was found
necessary to give up the idea.

However, after the completion of the tests of the launching apparatus some
experiments were made in flying the model as a kite. For this purpose a mast
twenty feet high was constructed and so arranged that it could be mounted at
the center of a small power launch. The model aerodrome was flown by a cord
connected to it by a bridle, the cord passing over a swivel pulley on top of the
mast and down into the boat, whence it could be played out or hauled in as
occasion required. By heading the launch into the wind it was possible to se-
cure sufficient relative velocity to cause the model to support itself and a num-
ber of tests were made in this way. It was found that when the bridle was at-
tached at the point at which the propellers would deliver their thrust, had they
been in use and driven by power, the model flew exceedingly well, maintaining
its equilibrium even during very strong gusts. Owing to the rolling produced
by waves from the large boats which were continually passing in the part of
the river where these tests were made, the power launch was often in danger of
being upset by its tall mast; and finally, when the tests were just reaching the
point where accurate information was being obtained on the balancing of the
model, a sudden rolling of the boat caused the mast to snap off while the model
was in the air. Before it could be picked up from the water a passing boat had

swamped it and it was lost in the river.

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 1165)

Although the model was, as has been said, rudely constructed and, there-
fore, did not represent a serious loss, yet the pressure of the more important
construction work for the large machine prohibited the construction of another
rough model for continuing these kite experiments, which it was felt could not
at best be more than approximate indications of the general stability of the ma-
chine under practical conditions.

CHAPTER IV
HOUSE-BOAT AND LAUNCHING APPARATUS

The use of a house-boat seemed to Mr. Langley so indispensable in former
years in making open-air tests of the models that he decided from the outset,
though advised by the writer against doing so, to use the same plan on a much
larger scale in connection with the large aerodrome. Aside from its supposed
utility as a convenient and apparently safe place from which to launch the aero-
drome, the house-boat was valuable as a portable workshop for making neces-
sary repairs and as a temporary storehouse for the apparatus, thereby say-
ing much packing and unpacking. It also provided sleeping quarters for the
workmen.

Tt was early seen that this plan would require a boat at least 60 by 40 feet,
which could be built only at a large initial cost. But as the experience with mod-
els had so firmly convinced Mr. Langley that it was necessary not only that the
aerodrome be launched over the water, but also at a considerable height above it,
and from a station that commanded all points of the compass, he decided to
adopt this plan for the large aerodrome, and designs for such a boat were ac-
cordingly made in the latter part of 1898.

In order to insure the completion of this house-boat by the time the aero-
drome was expected to be ready for trial, it was built under contract. Imme-
diately after its delivery in May, 1899, work was begun on the superstructure
which carried the launching track. This superstructure was a considerable un-
dertaking, involving a turn-table weighing about 15 tons, supported on a double
cireular track, and this track in turn was supported entirely from the side walls
of the house to avoid having columns in the middle of the floor. From the pho-
tographs, Plate 38, Figs. 1, 2 and 3, it will be seen that the entire superstructure
was supported by three trussed girders extending across the boat above the
roof and earried by vertical posts built into the side walls of the house. The
turn-table was 48 feet square and the launching track carried by it was 5 feet
gauge by 80 feet long.

In making tests of the models, it had been the practice to carry the main
body of the aerodrome up a ladder to the upper works of the boat, the wings
being also carried up in the same manner. As the large aerodrome was ex-
pected to weigh at least 640 pounds, of which 350 pounds would be the steel
frame with its undetachable parts, such as the engine and its appurtenances, it
was seen that something more effective than a ladder would need to be provided
for getting the aerodrome from the interior of the boat to the launching track

156

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 38

Fic. 3.

HOUSE-BOAT AND LAUNCHING APPARATUS, 1899

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT ilSy//

above. It was therefore decided to place the upper works of the boat rather
nearer the rear end than the front, thus leaving a space over the front end of
the house through which a large trap-door might be cut in the roof, and it was
thought that in this way the aerodrome might be passed up to the launching
track by the use of suitable ropes and pulleys. The upper works were so ar-
ranged, and a sliding trap-door was provided in the roof, but more intimate
knowledge of the difficulties of handling so large and heavy a frame made it
certain, even before the aerodrome was ever placed upon the house-boat, that
it would be impossible to transport it to the upper works by passing it through
the trap-door. <A different plan was then resorted to. A very large door was
constructed at the rear end of the house, through which the completely assem-
bled frame could be carried in a level position and placed upon a large raft,
consisting of a lattice flooring over pontoons, moored at the rear end of the
boat, as clearly seen in Plate 38. In order to raise the aerodrome frame from
the raft to the upper works, a large, but light, mast and boom, with suitable
stays were provided. As the wings, when mounted in their proper position
on the aerodrome, would be interfered with by such a mast, the mast and boom
were so devised as to be capable of rapid erection and dismounting, only five
minutes being necessary for either operation. In Plate 38 the mast and boom
are seen in position in Fig. 3, while in Figs. 1 and 2 they have been dismounted.

The construction of the launching track and car was begun in November,
1899, but their completion was long delayed, as they were frequently put aside
for the more immediately important parts of the work. Moreover, the arrange-
ment of the struts and clutch of the launching car depended entirely on the form
and dimensions of the frame of the aerodrome, which could not be entirely de-
cided until a proper engine had been secured and tested in the frame to deter-
mine what modifications of it were necessary. In the spring of 1902, however,
the launching car was entirely finished and a number of tests of the large engine
were made in the shop with the frame mounted in position on the car.

From the description of the ‘‘overhead ’’? launching apparatus (Part I,
Chapter X) which had proved so successful in the tests of the models, both in
1896 and in the later experiments of 1899, it will be recalled that the essential
features of it were a track and a light car with three hinged struts which ex-
tended below the body of the car, and against which suitable co-acting bearing
points attached to the frame of the aerodrome were tightly drawn by means of
a cluteh which gripped a special fitting fastened to the aerodrome frame near
the central point of its length. After the engine of the aerodrome had been
started and got to running at full speed, the car was released and moved for-
ward along its track by the combined force of the thrust of the propellers and
the pull of the coiled launching springs. Just before the car reached the for-
ward end of the track, a cam at this point caused the clutch to open and release

158 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

the aerodrome, which immediately dropped slightly, as it had purposely not
quite reached a speed sufficient to cause it to soar. This slight drop of the
aerodrome, even if it were only a fraction of an inch, made it possible for the
hinged struts, against which it had been held by the clutch, to be folded up by
their special springs against the floor of the car, thus leaving the aerodrome
free in the air without danger of entanglement.

The struts referred to above were three in number, two being placed near
the rear and one at the center of the front of the car. The use of three points
of support had the advantage of furnishing a rather rigid foundation against
which the frame could be tightly drawn by means of the clutch-hook without
risk of straining it. In designing the ‘‘ underneath ’’ launching apparatus, which
was very thoroughly tested in the experiments with the models in the summer of
1899, the plan of having three struts with the aerodrome drawn tightly against
them by means of a central clutch-hook was continued with most satisfactory
results.

When the position of the struts on this launching apparatus had been
changed so as to permit it to be used for the quarter-size model, it was found, in
making shop tests of the engine with the aerodrome mounted on the launching
car, that, owing to the greater vibration produced by the gasoline engine, the
three points of suspension did not hold the model in a sufficiently rigid manner.
It became necessary, therefore, to use four struts, the two rear ones being left.
as before, and the single one in front being replaced by two interconnected ones
arranged similarly to those in the rear. After making this change no difficulty
was found in holding the aerodrome rigidly against the struts, and this modifi-
cation was therefore immediately introduced in the designs for the large launch-
ing car which was already under construction.

Experience, both with models 5 and 6, and with the quarter-size model, had
also demonstrated the necessity of providing some means whereby the aero-
drome frame would be relieved of the torsional strains produced upon it by a
side wind striking the under surface of the wings when the aerodrome was
mounted on the car preparatory to a test. The means for preventing these tor-
sional strains in the ease of the models, when the ‘‘ overhead ’’ type of launch-
ing car was used, has been described in Chapter X of Part I. However, with
the ‘underneath ’’ type of launching ear, a different means was necessary. A plan,
in which outriggers projected from the body of the car and wires running from
these outriggers up to the main ribs of the wings, with means for releasing
the wires just before the car reached the end of the track, was used with the
‘« underneath ”’ car in the tests of models 5 and 6 in the summer of 1899, but the
outriggers were frequently deranged by the sudden stopping of the car at the
end of the run and they were replaced by a simpler arrangement. In this plan
the torsional strains were relieved by providing, at the forward and rear ends

VOL. 27, NO. 3, PL. 39

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

METHOD OF ATTACHING GUY-WIRES TO GUY-POSTS TO RELIEVE TORSIONAL STRAIN

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 159),

of the ear, smaller hinged uprights furnished in their upper part with a small
slot into which a pin projected from the bottom of the forward and rear guy-
posts, respectively. The guy-wires from the wings being connected to the
lower ends of the guy-posts the torsional strain produced by a side wind was
immediately transmitted from the wings through the guy-wires to the guy-post,
whence it was transmitted to the car itself, and thus prevented from acting on
the metal frame of the aerodrome, as shown in Plate 39. These additional short
struts for taking up the torsional strain were first added to the small launch-
ing car in 1901, and in the succeeding tests made with the quarter-size model
no trouble of any kind was indicated as likely to be caused by them. <As it was
these extra struts which were directly responsible for the accident in the launch-
ing of the large aerodrome October 7, 1903, at the time of its first trial, and pos-
sibly also for that on December 8, 1903, at the time of the second trial, special
attention is here called to them.

The length of travel which could be provided for the launching car in the
ease of the large aerodrome, as well as in that of the models was necessarily
very limited, owing to the fact that the track had to be constructed on the top of
the house of the boat. It was therefore necessary, in order that the aerodrome
might attain a speed sufficient for soaring before being launched, to keep the
weight of the launching car as small as possible, a given spring tension being
capable. of accelerating a given mass a definite amount in a given length of
travel. With a heavier launching car the spring tension would have to be in-
creased. Moreover, since the blow which would be struck when the car was sud-
denly stopped at the end of the track, would depend on its mass as well as its
velocity, there was an additional reason for trying to keep the weight of the
car as small as possible.

While it was found perfectly feasible to keep the weight of the launching
ear for the model low enough for practical purposes, in designing the launching
ear for the large aerodrome it was only by eliminating all flooring of the car
and providing merely a box frame with necessary cross-braces, that its weight
was kept within what appeared reasonable limits. Even then the blow which it
would strike when it reached the end of the track was found by calculation to
be exceedingly formidable.

Referring to the drawings of Plate 40, Figs. 1, 2 and 3, it will be seen that
the large launching car consisted essentially of two parallel longitudinal side
members 6 inches deep by 1.5 inches thick by 19 feet long, connected by three
main sets of cross-members: one set near the rear, at the point at which the
rear struts for supporting the aerodrome were mounted ; a second rather heavier
set about the middle of its length, at the point where the strut which carried
the elutch-hook was mounted; and a third near the front, at the point where the
front struts were mounted. Projecting from the forward end of each of the

160 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

longitudinal side members were piston rods, on which were mounted leather-cup
pistons, which co-acted with buffer cylinders fixed at the extreme front of the
track to absorb the blow when the car reached them at the end of its travel.
The car was supported on each side by means of four hangers (Figs. 4 and 5)
which carried grooved wheels having ball-bearings and running on a steel track
consisting of flat plates fastened on the side of the timbers of the launching
track. On the extreme lower point of these hangers were small guide pulleys,
so placed as to be just below and out of contact with a guard rail on the side
of the launching track, thus preventing any possibility of the launching car be-
ing raised from the track either during its forward motion or by a side wind
striking underneath the wings.

On the large launching ear the arrangement of the struts against which the
bearing points of the frame were tightly drawn by the clutch was similar in all
respects to that used on the model car, there being only slight differences in
details. The details of the uprights on which the bearing points of the aero-
drome frame rested are clearly shown in Figs. 6, 7, 8, and 9 of Plate 40. From
the photographs (Plate 41, Figs. 1, 2, and 3) which show the large frame
mounted on the launching car, the general arrangement of the struts and the
clutch-hook can be readily seen; and from Plate 42, Figs. 1, 2, and 3, which show
in detail most of the important features of the clutch-post and its cluteh, a very
vood idea of the size of the different parts may be had by observing that the
distance from the fulerum of each half of the hook to the pin by which it was
connected through the universal joint to the vertical rods is five inches. As
previously stated, this cluteh-hook gripped the lower pyramid and pulled the
bearing points of the frame firmly against the forward and rear struts of the
launching ear, and in launching the aerodrome the triggers arranged on the
bottom of the car, which at the proper time pull on the vertical rods and thereby
foree the two halves of the clutch-hook apart, are so arranged that they strike
4 cross-beam at the front end of the track one inch before the triggers, which
keep the struts from being pulled down by their springs, which tend to fold
them up and force them down against the car. The triggers, which prevent the
struts from being folded down, strike a cross-beam in the track one foot before
the buffer pistons on the end of the car begin to enter the buffer cylinders at
the end of the track, and, consequently, one foot before the folding prop, which
supports the front end of the track, is knocked out by the car striking a special
trigger which allows this folding prop to swing forward when the front end of
the track folds down to insure that the aerodrome will not become entangled
with the car, even though the aerodrome be not quite up to soarig speed at the
moment of launching. The manner in which this front end of the track folds
down can be very readily seen by comparing Plate 43 with Plate 95 of Chapter
XII, the former showing the front end of the track in horizontal position, with

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 40

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General Plan & etatls of Launching Car.
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GENERAL PLAN AND DETAILS OF LAUNCHING-CAR

15

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 41

AERODROME ON LAUNCHING-CAR

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 42

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Details of Clutch Pest for Launching Car.
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DETAILS OF CLUTCH POST FOR LAUNCHING-CAR

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 43

ee,

IV iy oa | 1 Bs .

FRONT END CF TRACK JUST PREPARATORY TO LAUNCHING AERODROME

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 161

the aerodrome at the extreme rear end just preparatory to launching, and the
latter showing the front end of the track folded down with the hinged prop
standing outward in its downward path and the aerodrome just launched. These
photographs will be more particularly referred to later, but attention is here
ealled to them so that the description immediately following may be more
easily understood.

Although this method of launching the aerodrome seemed to Mr. Langley,
both theoretically and from the experience with the modeis, to be a satisfactory
and feasible plan, there were two very important respects in which it seemed
from the very first open to objection. In the first place, it was necessary that
the aerodrome should be launched as nearly at its soaring speed as possible,
because either an excess or deficiency of speed interfered to some extent with
the equilibrium of the machine. So many factors were involved in the deter-
mination of what this final velocity should be that it seemed almost impossible
to be sure of the results until at least one test of the aerodrome had been made.
In the second place it was not known whether the rapid acceleration of the car
would seriously interfere with the equilibrium of the aviator.

In reference to the first question it was, of course, known that a freely
falling body acquires a speed of 32 feet per second at the end of the first sec-
ond after having fallen a distance of 16 feet. It was proposed to launch the
aerodrome at approximately 35 feet per second; and, since the distance over
which the car would pass in acquiring this speed was approximately 60 feet, the
rate of acceleration would, of course, be less than that for a freely fallmg body.
The conditions in the two cases, however, are quite different. In the case of
the freely falling body there is the constant force of gravity which causes the
acceleration. In the case of the aerodrome the car is initially standing still but
ready to be acted upon by the combined force of the thrust of the propellers

-and the tension of the springs. The propeller thrust is approximately 450 pounds
at the moment of releasing the car, while the spring tension adds approximately
400 pounds more pull, giving a total pull of 850 pounds acting on the car at the
start. The weight of the aerodrome including the aeronaut bemg approximately
850 pounds, and the weight of the car being approximately 450 pounds, the total
weight to be accelerated is 1300 pounds. The resistance of the car and the aero-
drome is zero at the moment the car is released, and increases approximately as
the square of the velocity until it reaches approximately 300 pounds at the soar-
ing speed of the aerodrome; while on the other hand the spring tension de-
creases uniformly from 400 pounds at the start to approximately 76 pounds at
the end of the track, and the thrust due to the propellers decreases from 450
pounds at the start to approximately 250 pounds at the moment of launching.
Consequently, it is in a general way clear that the rate of acceleration of the

aerodrome and car decrease, probably in a geometric ratio, the rate of accelera-
16

162 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 2
tion at the moment of launching the aerodrome being much less than that of a
freely falling body. Since so many factors enter into the problem no confidence
was felt in calculations as to what the rate of acceleration would be. It was,
therefore, decided to determine it experimentally at the same time that tests
were made on the car to determine what spring tension would be necessary to
enable the aerodrome and car to acquire soaring speed by the time they reached
the end of the track.

It was obviously impossible to make this initial test with the aerodrome
mounted on the launching car, as the aerodrome would certainly wreck both it-
self and the car were it allowed to remain fastened when the car was stopped
at the end of the track. It was, therefore, decided to make the tests by mount-
ing on the car boards which would have a head resistance equal to that of the
aerodrome. In order to minimize as much as possible the blow due to the
car striking the buffers at the end of the track, the car had been made as
light as possible. On this account it was felt to be unwise to risk adding to it
a weight of 850 pounds to represent the aerodrome, and supplying an addi-
tional spring tension to represent the thrust of the propellers, as the total effect
of the added weight and the added pull would certainly completely demolish the
car. By caleulation it was found that the omission of the 850 pounds weight of
the aerodrome and the spring tension to represent the thrust of the propellers
would practically counterbalance each other; and that if sufficient spring tension
were provided to cause the car, with the light boards representing the head re-
sistance of the aerodrome, to reach the soaring speed by the time it arrived at
the end of the track, it would be safe to assume that this spring tension would
be sufficient for use in launching the aerodrome.

The method of measuring the final speed of the launching car for the mod-
els consisted in fastening a strip of smoked paper to the launching car in such
a position that it was drawn past a stylus fastened to the end of a vibrating
tuning fork placed at the end of the track. This had proved perfectly success-
ful, but it gave a record merely of the final speed attained by the car at the mo-
ment of launching the aerodrome. In the case of the large aerodrome it was de-
sirable to have a record of the speed of the car during the first few feet, and
also at several other points in its travel down the launching track, and the more
numerous these points the better. Short strips of copper were accordingly
placed every twelve inches along the length of the track, and these were con-
nected by a wire to one terminal of a small electric battery. Mounted on the car,
in such a way that it would be drawn across these contact strips, was a copper
brush arranged to make continuous contact with another wire stretched along
the track, this second wire being connected to the other terminal of the electric
battery and having in its cireuit the magnet which actuated a pen on a chrono-
graph. Since the rate of revolution of the chronograph barrel was known, the

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 163

distance between the marks which the magnet would cause the pen to make when
its circuit was closed by the brush on the car passing across the contact strips
on the track would give correct measures of the time consumed by the car in
passing over each twelve inches of its travel. Upon test, however, it was found
impossible to get the chronograph magnets to work rapidly enough to respond
to the very rapid opening and closing of the circuit after the car had passed
over the first one-quarter of its length of travel. As a large part of the slowness
of action seemed to be due to the weight of the fountain pens, they were re-
placed by small glass tubes drawn out to a fine point and containing a small
amount of ink. These seemed, however, to be still too heavy to respond to the
rapid closing of the circuit unless the contacts were made unduly long. The
contacts were finally made three inches long and placed only every three feet
along the track, but just as these contacts were completed and placed in posi-
tion the clock-work of the chronograph itself became deranged. Before it could
be repaired, the tests were discontinued, as everything was in readiness for the
boat to proceed down the river where the actual tests in free flight were to be
made. Tests of the final speed of the car were, however, made by the tuning-
fork method, and the springs were adjusted until their tension was sufficient
to-cause the car to attain a speed of thirty-five feet a second at a point three
inches in front of the point at which the aerodrome would be released from the
car.

CHAPTER V
CONSTRUCTION OF FRAME OF LARGE AERODROME

The general plan for the large aerodrome was never a matter of uncer-
tainty. At the time when the first general designs were made there had been in
the history of mankind only one type of machine, that of the steam-driven Lang-
ley models, which had proved capable of flight for any considerable distance.
Furthermore, the selection of this type had been the result not of sudden fancy
or of purely theoretical consideration, but of years of the most careful experi-
mentation, in the course of which nearly every conceivable style of machine had
been tested with some form of power. It would have been worse than folly,
therefore, if the one clear path had been left to seek some unknown way.

It was fully realized from the first, however, that the increase in size alone
would make necessary in the design for the large aerodrome a great many mod-
ifications from the designs of the steam-driven models. It was not possible here,
as in nearly every other kind of structure, simply to magnify uniformly the
parts and proportions of the small machine in order to obtain a successful large
one. This is particularly true in the case of the aerodrome, because the rapid
increase of weight in the larger structure is out of all proportion to the increase
in strength, while it is very desirable that the more expensive machine which is
designed to carry a human being shall be relatively even stronger than the
easily replaced model. This problem of increasing size without sacrificing
strength and stability, it was known from the beginning, would be encountered
in a particularly difficult form in designing the frame of the large machine, and
was to be solved not by the discovery of some new and wonderfully strong ma-
terial, but by improvements both in the general plan and the details of the ma-
chine. Here, as is often the ease, it was not the large changes in the design but
the improvements in small and sometimes seemingly unimportant details which
demanded the most careful consideration and, as a whole, contributed most to
the final result. For this reason, as well as because the large changes, when
pointed out, are usually easily understood, the present chapter is for the most
part a description of the improvement of details.

From the experience gained in the construction of the frames of the sev-
eral steam-driven models, it was decided that the frame for the large aerodrome
must consist essentially of two principal parts. First, a rigid backbone was re-
quired, extending from the point of attachment of the front wings to the point
of attachment of the rear wings; and this backbone, for convenience designated

164

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 165

the ‘‘ main frame,’? must support the second principal part, the ‘‘ transverse
frame,’’ which formed a cross with the main frame, and at the ends of which
the propellers were mounted. While it was necessary that this transverse
frame should have considerable rigidity and strength in a vertical direction,
yet its main strength and stiffness was required in the horizontal plane for
withstanding the thrust of the propellers. It had been possible to construct
the frames of the later steam-driven models stiff enough, and at the same
time light enough, by the use of properly proportioned steel tubing, but caleula-
tion very soon showed that in order to secure sufficient rigidity for the frame of
the large aerodrome and at the same time keep the weight within the permis-
sible limit, it would be necessary to depend very largely on euy-wires and to
use tubing only for forming the struts against which the guy-wires should act.
But this obviously introduced a new series of problems. The extensive system
of guy-wires necessary would add materially to the head resistance of the aero-
drome, and this might conceivably be so great as to require more propulsive
power than would be required for a frame heavier but unineumbered by the
head resistance of the wires. It became necessary to consider these problems,
but no data were accessible from which the head resistance could be computed
with any confidence. The coefficient of resistance for a eylindrical body moving
through the air ina direction perpendicular to its length may in general be taken
as one-half that of a flat body of the same cross-section; but it was thought
very certain that, owing to the fact that tightly stretched wires are in constant
vibration when the aerodrome is in the air, the resistance of the wires must
be considerably greater than would be calculated from treating them as eylin-
ders having a coefficient of 0.5. Unfortunately, no data on the resistance of vi-
brating wires were at hand. Before proceeding with the designs for the guy-
ing of the frame, therefore, the following brief series of tests was made in
November, 1898, on the whirling table, in order to learn approximately the resist-
ance that the proposed system of guy-wires for the large aerodrome would
offer:

MEASUREMENTS OF THE RESISTANCE OF GUY-WIRES, USING FRAME ATTACHED TO

“ BALANCE.”

RESISTANCE OF FRAME WiTHoutT WIRES.

Frame consists of: 4 tubes, 1 cm. diameter, 14.5 cm. long; 2 tubes, 1 em. diameter, 41 em. long; 2
tubes, 1 em. diameter, 101 cm. long.

Revolutions of Velocity of - Resistance. Calculated resis-
turn-table per frame. Feet Grammes. tance of frame.
minute. per minute. fr. Grammes.
6.75 608 11.5 14.2
9.75 877 34.0 29.6
12.0 1080 51.8 44.8
16.35 1475 97.0 83.8
19.75 1775 134.0 121.3
22.7 2045 168.0 161.2

25.5 2290 205.0 202.0

166

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

vou. 27

RESISTANCE OF FRAME WITH Ist SET OF WIRES.

First set of wires: 16 wires, 0.6 mm. diameter, 102 cm. long; 6 wires, 0.6 mm. diameter, 42 em. long.

Revolutions of
turn-table per
minute.

ae!

oO bo & to te
“Ic ol ol
on

-mwonw o
ir)

bo

Velocity of

wires. Feet
per minute.

877
1080
1237
1550
1822
2025
2060
2215

Resistance of

frame and wires.
R,.

Grammes.
47.5

723.5

93.5
144.0
187.0
216.0
225.0
250.0

Resistance of

Calculated resis-

wires. tance of wires.
R,-—r=n. Grammes.
13.5 8.88
21.7 13.47
25.5 17.65
37.0 27.7
45.5 38.4
47.5 47.4
52.0 49.0
56.5 56.7

RESISTANCE OF FRAME WITH 2D SET OF WIRES.

Second set of wires: 15 wires, 1.2 mm. diameter, 102 cm. long; 2 wires, 1.2 mm. diameter, 42 cm. long.

Revolutions of
turn-table
per minute.

9.25

9.35
11.8
11.5
13.0
13.15
16.7
16.75
19.5
19.7
21.60
21.65
21.75

Velocity of
wires. Feet

per minute.

833

841
1018
10385
1170
1185
1505
1510
1755
1770
1945
1950
1957

Resistance of

frame and wires.

Grammes. Rp.
54.0
55.0
82.0
82.0

104.5
105.0
160.0
160.0
196.0
203.0
236.0
237.0
235.0

Resistance of

wires.

Calculated resis-
tance of wires.

Re—Tr=re. Grammes.
26.5 15.35
27.0 15.4
36.75 22.65
35.25 23.4
43.0 29.9
42.5 30.60
59.0 49.5
58.0 49.9
64.0 67.4
69.5 68.5
77.0 82.6
77.75 83.2
15.5 83.7

RESISTANCE OF FRAME WITH 3D SET OF WIRES..

Third set of wires: 15 wires, 2 mm. diameter, 102 cm. long; 2 wires,

Revolutions of
turn-table
per minute.

9.25
11.55
11.55
15.25
18.1
19.25
19.25
20.63

Velocity of

wires. Feet

per minute.
833
1040
1040
1375
1630
1735
17385
1860

Resistance of

frame and wires.

Grammes. R3.
65
91

101

160

203

221

216

237

Resistance
wires.
R3—T=T3.

37.5
43.5
53.5
75.0
86.5
92.0
87.0
90.5

2 mm. diameter, 42 em. long.

of Calculated resis-
tance of wires.
Grammes.

25.2
39.35
39.35
68.7
96.6
109.5
109.5
125.8

The last column of these tables is caleulated for a coefficient of form equal
to 0.5, which has been found to be approximately correct for a rigid cylindrical

body.

These tables are not sufficiently extensive to determine accurately the ex-
act resistance that wires of various sizes will offer at given velocities, or to
serve as the basis for the deduction of formule, and were not made for that
purpose. However, from the above data, and the curves plotted in Plate 44,
it will be seen that some unexpected results were obtained.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 44

1800

1700

BiriL

=H ia
CL aZ
SO

1300 /|

A JFRAME] WITHOUT w es |

FRAME| WITH]! 2° SET OF WIRES

eee ee
wl Lhe [dot | Le Prete pe
oT a SS is 2
oy as eee

25 50 75 125 150 \75 200 225 250 275 300
RESISTANCE OF WIRES AT GIVEN VELOCITIES

ORDINATES—=VELOCITY IN FEET PER SECOND
ABSCISSAE = RESISTANCE IN GRAMMES

a

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 167

These results are fairly well summarized in the following general state-
ments: First, that the coefficient of resistance increases to some degree as the
size of the wire is decreased; second, that in the case of wires of the size which
it was expected to use, and at approximately the soaring speed of the aero-
drome, the resistance is certainly not greater than 75 per cent, and more prob-
ably less than 50 per cent of the resistance encountered by a flat surface of the
same projected area; third, that the coefficient of resistance did not seem to be
increased by the vibration of the wires. On the contrary, it was noted during
the experiments that when they reached a speed which just caused them to
*« sing,’’ there was a marked diminution in the resistance. This statement is
made, however, with some reserve, for it is probable that the singing of the
wires was due to vibration in the horizontal plane, and it is not definitely known
what the effect would be of vibration in the vertical piane.

To make the very extensive experiments necessary to determine these prop-
ositions conclusively would have required much more time than could at this
period be spared from the actual constructional work on the aerodrome. Never-
theless, the data did seem to indicate that it was at least not unwise to employ
the extensive system of guying which had been planned in order to give the nee-
essary strength to the frame of the large aerodrome. This pian of construction
was, therefore, definitely adopted, and as a result of later experience the sys-
tem of guying was still further extended.

As the transverse frame had to be made comparatively rigid in order to
prevent undue binding of the bearings of the transmission and propeller shafts,
it was necessary to make it intrinsically stronger and, therefore, heavier in
proportion to its size than the main frame. The main frame, although requir-
ing great strength to enable it to withstand the strains, both torsional and di-
rect, which were imposed upon it by the weights which it supported, did not
need excessive rigidity, and could, indeed, be distorted an appreciable amount
without danger of any serious effect on the action of the wings or rudder; but
even a small amount of distortion in the transverse frame might easily cause
such friction at the bearings of the shafts as to absorb fifty per cent or more of
the engine power.

In the photographs, Plates 45 to 48, which show the actual condition of the
frame on January 31 and February 1, 1900, the letters A, B, C, D, FE, F, G, H
and J designate parts of the main frame, A and H being the rear and front mid-
rods, respectively, to which the wings were to be attached. B and J are curved
extensions of the starboard main tube, the port main tube being exactly sim-
ilar, and C, D, E, F and G are cross-tubes which connect the midrods to the port
and starboard tubes. R is the front main tube of the transverse frame, the rear
main tube being exactly similar, and both being connected to the main tubes
of the main frame where they cross them. The ends of the main tubes of the

168 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

transverse frame are joined together by the ‘‘ bed plates ’’ L, which are of L
beam section, and have mounted on their outer faces the bearings which sup-
port the propeller shafts. At V are bevel gears mounted on the propeller shafts,
which are driven by co-acting bevel gears, M, mounted on the outer ends of the
transmission shafts, O, the latter being at this point firmly supported in bear-
ings mounted on the inner faces of the bed plates and steadied by the intermedi-
ate bearings, N. The two transmission shafts are seen to be not in line, the ro-
tary cylinder engine that was then under construction requiring this arrange-
ment. The bed plates, L, are further stiffened by the brace tubes, K, and the
transverse frame is braced against the thrust of the propellers by the tubes J.
The four tubes, P, unite at their upper ends to form what was designated as
the upper ‘‘ pyramid,’’ and the wires, § and 7, radiate from its apex to the
rear and front, respectively, of the main frame. The lower ‘‘ pyramid,’’ on the
under side of the frame, also has similar wires running fore and aft. The
main portions of both frames are further strengthened by their sub-frames,
which merge together, and the main tubes of the main frame are individually
stiffened in the vertical plane by a minor system of guying. The scales shown
in the photographs are calibrated in metres.

It is to be particularly noted that the midrod, which had heretofore formed
the backbone of the main frame, was now made to act merely as a means of at-
taching the wings to the frame, the main strength of the frame being furnished
by the two parallel fifty millimetre tubes which extended the entire length of
the frame and which, reinforced by the guy-wires, formed a truss not only more
rigid transversely, but also many times stronger in its ability to resist torsional
strains than could be secured by a single tube of equal weight. In this plan of
constructing the main frame, the pyramids constituted a very important ele-
ment, for with the guy-wires arranged as they were it was impossible for any
portion of the frame to experience a stress which was not transmitted in some
way to the pyramids. In the frame, as here shown, these pyramids were
formed of tubes 15mm. in diameter, 0.5mm. thick, stiffened against buckling
under the end pressure by means of the cross-braces, which united them near
their midpoints. While the sole function of the upper pyramid was to serve
in the system of guying the frame, the lower pyramid not only served a similar
purpose, but also provided a means for holding the aerodrome to the launch-
ing car in the process of launching it, the clutch-hooks gripping around the
short horizontal tube at the apex of the pyramid and thus drawing the ‘‘ bear-
ing points ’’ of the machine firmly against the uprights on the car. In fact, the
particular arrangement of these pyramids was largely determined by this neces-
sity for providing means for holding the aerodrome to the launching ear, and
the form which seemed best suited to the purpose was duplicated on the up-
per side of the frame.

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 169

The ‘‘ bearing points ’’ were not attached to the frame at the time these
photographs were taken, but are seen leaning against the scales in the fore-
ground of Plate 46. Their position on the frame will be more clearly seen in
later photographs, where it will be noted that they were made use of in the
more elaborate system of guying which was adopted.

While, in general, the frame at this time seemed to be reasonably stiff and
strong, yet it was subjected to a very thorough test by supporting it at differ-
ent points and suspending from it weights to represent the various parts, such
as engine, aviator, wings, rudder and so forth, the deflections which were pro-
duced by these weights being carefully noted. It was further tested by subject-
ing it to vibratory strains, such as it would be likely to meet in actual use. After
this the whole frame was tested against torsional strains, such as would be
caused by the wind twisting one set of wings more than the other. As a result
of these tests it was decided that the frame should be strengthened as far as it
was possible to do so without greatly increasing the weight, which even now
was found to be rapidly increasing beyond what had been calculated as permis-
sible. The main guy-wires were replaced by heavier and stronger ones, and
while these were found to add somewhat to the stiffness of the frame, yet some-
thing more seemed necessary to insure safety.

The delay in securing the engine, which had been contracted for with a
guarantee that it would be delivered in February, 1899, had become so serious
and had delayed the completion of the frame to such an extent that the ques-
tion of building an exact duplicate of the large machine, but of one-quarter its
linear dimensions was being carefully considered at this time, and it was decided
to make no further changes in the guying of the large frame until after the
small one was built. On account of its smaller size changes could be more
readily and cheaply made on it, and the advantages of different methods of
guying could be just as well studied. Later, when this was completed, it was
found that, with the same system of guying that had been used in the larger
frame, the model was so very stiff that it did not require any further strength-
ening, the smaller scale, of course, accounting for the difference. What was
thought to be the best system to follow in strengthening the frame of the large
machine was, however, first tried on the smaller one, and it was found that for
a very slight increase in weight a very great increase in strength could be ob-
tained. This change in the system of guying consisted essentially of building a
‘‘ trestle? of tubing at a point on the upper side, midway between the pyramid
and the rear end of the frame. One of the former sets of eny-wires which
passed to the rear of the frame was then replaced by a set which started at the
foot of the rear tubes of the upper pyramid, passed over and was fastened to
the trestle, and from there passed to the rear end of the frame at the points
where the longer guy-wires from the pyramid had formerly been attached. The

170 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

euy-wires on the lower side of the frame, at the rear, were correspondingly
changed so that the upper and lower systems should be similar, the wires which
started from the main tubes at the foot of the pyramid passing to the bearing
points, and from there to the rear end of the frame.

In order to keep the main frame of the large aerodrome as short as pos-
sible, it had originally been planned to make the distance between the center of
pressure of the front wings and the center of pressure of the rear equal to five
metres. When these same proportions were followed in the quarter-size model,
it was found that it brought the rear wings so close to the propellers that their
lifting effect was certain to be interfered with by the blast of air created by the
slip of the propellers. It was therefore decided that all things considered it
would be best to increase this distance between the wings, even though this in-
volved an increase in weight, partly on account of the increased amount of
tubing, and still more on account of the guy-wires which it would be necessary
to add in order to make up for the weakness due to increased length. The large
aerodrome frame was accordingly lengthened 2.5 feet (76.2 cm.), and the guy-
wire system was changed to that clearly shown by the photographs of July 10,
1902, Plates 49, 50 and 51, the black cross-lines on the background being 50
centimetres apart. From an inspection of these photographs it will be seen that
two sets of guy-wires were carried from the upper and lower pyramids, re-
spectively, towards the rear of the frame, the first set being carried to the main
tubes at the foot of the ‘‘trestle ’’? and the bearing points, and the second set to
these same main tubes at the second cross-tube. The sets of wires which started
from the feet of the pyramids were carried over the ‘‘ trestle ’’ on the upper
side and the bearing points on the lower side, and both joined to the main tubes
at the rear cross-tube. Additional cross-guy-wires for stiffening the frame side-
ways were added in each of the squares formed by the junction of the cross-
tubes with the main tubes. A secondary system of truss guy-wires running
over short guy-posts attached to the tubes of the main frame also contributed
to the strength and rigidity of the whole.

Although the pyramids had shown no signs of weakness, nevertheless, be-
cause of increased strains due to the lengthening of the main frame, it was thought
advisable to make them stronger. Instead of the 15-mm. tubing, which had for-
merly been used, 25-mm. tubing of the same thickness was therefore substi-
tuted, and additional cross-braces were added, as will be seen from the photo-
graphs, and from the scale drawings in Plates 52, 53 and 54, which show the
aerodrome as it was when completed. The numerals attached to these draw-
ings refer to the detail drawings shown in later plates.

Tn order to seeure the proper adjustment of the guy-wires, not only of the
frame but of many other parts, notably the wings, propellers and rudder, it
was necessary to use a large number of turn-buckles. As almost every wire

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

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VOL. 27, NO. 3, PL. 54

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT ity

required at least one, and in some cases two turn-buckles, the weight repre-
sented by this single item rapidly became so formidable as to require serious
attention. In the construction of the models, it had been necessary to employ
some special turn-buckles in connecting the guy-wires of the wings to their guy-
posts in order to secure the minute adjustment of the wires necessary to pre-
vent the wings from being warped and distorted by unequal and improper ad-
justment. These turn-buckles had been made in the Institution shops, as the
very lightest ones which could be secured in the market were from ten to twenty
times as heavy as it was necessary for them to be to provide ample strength.
In the construction of the large aerodrome, however, the large number required,
and the desire to complete the machine at the earliest moment, made it advis-
able to procure the turn-buckles, if possible, from outside sources, and a very
eareful search was accordingly made among the various dealers. After much
delay some bronze turn-buckles were secured which were very much stronger
for their weight than any others on the market, but upon testing them it was
found that while they weighed 45 grammes, their average breaking strength was
only 593 pounds. Previous experience had shown that turn-buckles which would
not break under a less load than 750 pounds could certainly be made to weigh
not more than 18 grammes. As even at this time it was realized that at least
100 turn-buckles would be necessary for the entire machine, the excess weight
which the heavy turn-buckles. would add was felt to be absolutely prohibitory,
and the construction of steel turn-buckles was immediately begun in the Insti-
tution shops. These turn-buckles were at first made in several sizes, and while
some few were at first made ‘‘ double ended,’’ most of them were threaded at
only one end, the other end being provided with a swivel-hook, or eye. They
were at first made of mild steel, the swivel-hooks, in fact, bemg made of wire
nails in order to utilize the head of the nail as a shoulder without the expense
of machining rod steel of a size large enough to form the shoulder. It was
found, however, that the weak point of this type of turn-buckle was the swivel
end, and most of those which were then on hand were made double ended by
removing the hook, tapping a left-hand thread into this end of the shank, and
fitting a threaded eye-socket in it. The guy-wires themselves were attached to
the eyes of the turn-buckles and to the fittings on the frame by twisting loops
at the ends of the wires, and although the very greatest difference in the strength
of a completed guy-wire may result from the way in which the loops are twisted,
_yet, after much training, the workmen were taught to twist these very uniformly,
following the plan which can be best understood by an inspection of the draw-
ings in Plate 55 which show the loops more clearly than they can be described.
After the loops had been properly twisted, soft solder was run all through the
twist in order to unite firmly the twists of the wire. Although special grades
of wire were found which showed very high tensile strength when the wire was

Ue: SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

tested without having loops formed in its ends, yet it appeared that the twist-
ing of these high-grade wires so seriously affected them that in the case of guy-
wires with loops at the ends, better final results could be obtained by using
softer grades of steel. The wire which was actually found best, after much ex-
periment, was a good grade of Bessemer steel of a medium hardness, which had
been ‘‘ coppered ’’ to prevent rusting. However, even with the softer grades of
steel wire, it was found that there were sometimes hard spots in the wire which
revealed themselves only upon test, and that when a hard spot occurred in the
twisted portion where the loop was formed, the final strength of the completed
guy-wire was sometimes only twenty-five per cent of what it should be. The
precaution was then taken to subject each of the completed guys to a test strain
at. least twenty-five per cent greater than it was calculated the wire would have
to stand in actual use, so that no accident from defective wires would be likely
to oceur.

Later on, however, much trouble was caused by the loops in the ends of
some of the guy-wires slipping, owing to the giving way of the solder which
had been run through the joint, the amount of slipping, while small, being suf-
ficient to alter completely the relative stresses on the various wires, thus caus-
ing distortion of the framework itself. In order to avoid this difficulty a new
method was devised of attaching the guy-wires to the turn-buckles and to the
fittings by which they were carried to the frame. This method consisted m
threading the ends of the guy-wires so that they could be inserted directly
in the threaded ends of the turn-buckles. The wires when connected in this way
to the turn-buckles showed absolutely no. slip, and the entire system gained
greatly in strength thereby. The only disadvantage which was found in this
new method of attaching the guy-wires to their fittings, was that if the wire was
bent very close to the fitting, it would break in the screw thread very easily.
But since most of the guy-wires when once attached to the machine are always
tight, and in fact, under more or less strain, there was in most cases no likeli-
hood of the wires being endangered by being bent close to the fittings. Since
the screw threads, which it was necessary to adopt in this new plan of connect-
ing the guy-wires, had to be very much finer than the threads which had been
used in the turn-buckles previously constructed, it was necessary to make new
turn-buckles, the others being too thin to permit of their being bored out, bushed
and re-threaded. The new turn-buckles were made of a much higher grade of
steel, and probably represent very nearly the maximum of strength for the min-
imum of weight possible without the use of some of the very much higher-grade
steels which have recently come on the market, but which are exceedingly ex-
pensive to work. By means of this improved plan of attaching the wires,’ it

1The drawings, Plate 55, which illustrate many of the fittings used on the frame, show the guy-
wires as attached by means-of loops twisted in their ends, these drawings having been made before
the final plan of attaching the wires had been devised.

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 173

was found possible to gain practically fifty per cent in the strength of the entire
system of guy-wires used on the frame.

Many small changes were from time to time made in the various small fit-
tings by which the guy-wires were attached to the frame, nearly all of these fit-
tings having been originally made of a very mild grade of steel owing to the fact
that it was so very much easier to work. At the time these fittings were made
it was constantly expected that a trial of the aerodrome would be possible very
soon, and it seemed necessary to expedite the work as much as possible and
avoid the delay involved in using grades of steel that would have been mate-
rially harder to work. As is always the case in work of this kind, retrospect
shows many instances where what was supposed to be a short cut to results
actually proved to be the longest path, but the work as a whole was remark-
ably free from imperfect parts which necessitated reconstruction.

In the construction of the frames of the models it had been customary to
fit the tubing accurately at the joints and to join it permanently together by
brazing, as this was not only the lightest form of joint that could be made,
but also the most expeditious method consistent with securing a strength of the
joint comparable with that of the tubing itself. The construction of the frame
by this method of brazing the joimts together permanently, offered, however,
several serious drawbacks: among them, that when a tube got injured it was a
considerable task to replace it, while the brazing of the new tube in place re-
quired extreme care to prevent the frame from being warped when completed,
as the tube became longer while very hot and contracted after the joimt had
set. Furthermore, the great heat required destroyed to a considerable degree

? a reduction of

the desirable qualities due to the tube being ‘‘ cold drawn,’
strength of something like 25 per cent being almost inevitable, even when the
brazing was most carefully done. It was, therefore, decided that in the con-
struction of the large machine all of the main joints should be made by a sys-
tem of ‘‘ thimbles,’’ and it was planned at first to make these thimbles by
brazing short pieces of steel tubing into the proper shapes and angles so that
they would accurately fit the tubes which were to be jomed. The construction
of the thimbles in this manner, however, seemed to involve an excessive amount
of work; and, as it was found that very thin castings of aluminum-bronze
could be obtained, which would show a tensile strength very nearly as great
as steel, it was decided to make up patterns for the thimbles and cast them of
aluminum-bronze.

The aluminum-bronze castings were obtained and properly machined to fit
the tubes, but when it was attempted to “‘ tin ’’ the interior walls of the thim-
bles it was found that the solder could not be made to stick to the bronze.
As a considerable amount of work had been expended on the machine work of
these thimbles much time and effort was spent in attempting to devise ‘‘ fluxes ”’

174 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

and solders which could be made to work with the aluminum-bronze, but the
final result was that the aluminum-bronze thimbles had to be abandoned. They
were replaced by similar castings of gun-metal of a slightly heavier section,
which at the time were thought to be very suitable for the purpose.

But, in finally assembling the frame after the changes described above had
been made, steel thimbles, built up of short pieces of tubing, as had originally
been planned, were substituted for the gun-metal thimbles. This change was
made not only because of the great increase in strength, but more particularly
because many of the gun-metal fittings had been imperfectly constructed, so
that it was extremely difficult to align the frame. The steel thimbles, which
were made in the Institution shops proved thoroughly satisfactory and gave no
trouble of any kind. Many of these thimbles and the method of attaching the
guy-wire fittings to them are shown in Plates 56 and 57, as well as in Plate 55.

TRANSVERSE E'RAME

It will be recalled from the description of the models Nos. 5 and 6, in Part
I, that the position of the line of thrust, with respect to the positions of the
center of pressure and center of gravity in the vertical plane was, theoretically,
very much better in No. 6 than in No. 5. In designing the large aerodrome,
it was desired to reproduce as nearly as possible the relative position of the line
of thrust with reference to the center of pressure and center of gravity which ex-
isted in No. 6, but for constructional reasons it was found impossible to do so. In
fact it appeared that without seriously complicating the construction of the frame
it was impossible to raise the line of thrust with respect to the center of gravity
materially higher than it was in No. 5. In No. 6 the line of thrust was 12 centi-
metres above the midrod, this being effected by placing the engines some dis-
tance from the boiler, and at the extreme ends of the transverse frame where
they were connected directly to the propellers. In the case of the steam engine
the weight of the engine proper is a relatively small portion of the entire
weight of the power plant, and it is, therefore, possible to put the engine al-
most anywhere without materially affecting the center of gravity. But where
a gas engine is used the engine itself constitutes the greater part of the weight
of the power plant, and any raising of the engine, therefore, materially raises
the center of gravity of the whole machine. The line of thrust in the large
aerodrome was, therefore, practically in the plane of the main frame, and con-
sequently very little higher than the center of gravity.

The use of one engine to drive two propellers mounted at opposite ends
of the transverse frame, and in a direction perpendicular to the crank shaft of
the engine, necessitates the use of a pair of bevel gears between each of the
propeller shafts and the shafts by which the power is conveyed to them from

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the engine shaft. Since the efficient transmission of power through bevel gears
requires that they be very accurately placed with reference to each other, and
maintained very accurately in this position while they are at work, it was nec-
essary to make the transverse frame very rigid, especially at its extreme ends.
This was accomplished by the use of what were called ‘‘ propeller-shaft bed
plates.’’ They are designated by the numeral 27 in Plate 54, and are shown
in detail in Plate 58 as of a very deep I-beam section, having very narrow
flanges top and bottom, the web of the beam furnishing the strength in a
vertical direction, while sufficient stiffness laterally was obtained from the flanges,
assisted by the brace tubes, which acted as struts between the bed plates and
the main tubes of the transverse frame. These struts, while very light, added
enormously not only to the lateral stiffness of the propeller bed plates, but
furnished for a minimum weight a maximum prevention against twisting of the
plates. The propeller-shaft bed plates were originally planned to be made
of sheet metal with the flanges brazed to the web. But at the time that they
were constructed the pressure of the work was so great in the Institution shops
that it was found necessary to have some of the work done outside, and the
parties who undertook the construction of these bed plates were unwilling to
attempt to braze them up, and accordingly worked them from steel forgings
made for the purpose. The expense of this plan of construction proved large
and unnecessary, as both previous and later experience proved that it was not
only practicable to’ braze up bed plates more complicated in their design than
these, but that equal strength for equal weight could thus be obtained for less
than one-quarter the cost of constructing them from solid forgings. Further-
more, where such parts are made from the solid, changes which later tests
prove advisable can frequently not be carried out without very serious cost
and delay, while with the bed plates formed by brazing less hesitaney is felt in
removing parts which are brazed thereto and substituting new parts, or even
discarding the bed plates altogether and substituting new ones. Particular em-
phasis is laid on this point for the reason that much expense and delay would
have been avoided had these very expensive propeller-shaft bed plates been dis-
carded as early as 1901 and replaced by others which would have permitted a
considerable strengthening of the ball-bearings, which, while strong enough to
stand even more power than they were originally designed for, were far too
weak to be safe when working under the greatly increased stress due to the
very much higher engine power which was later used. Instead of discarding
these bed plates then for new ones, they were strengthened by brazing to them
erescent-shaped pieces, as shown in the drawings and photographs. This
strengthening was made necessary by the larger hole cut in the bed plates for
the larger bevel gears. The bed plates for the engine, which are later de-
scribed, besides other Fed plates which were made for other purposes, were all
19

176 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 2
formed by the use of sheet metal and tubing properly brazed together, and
none of them ever gave any trouble.

In the early photographs of the aerodrome frame, especially that of Jan-
uary 31, 1900, Plate 45, it will be noted that the two transmission shafts, which
extend from the propeller-shaft bed plates towards the center, are not in line,
the port transmission shaft being at the center of the transverse frame, while
the starboard one is three inches to one side. This arrangement was neces-
sary in order to connect the shafts to the rotary cylinder engine which was
being constructed under contract, and which was almost momentarily expected
for more than a year after its original promise of delivery on February 28,
1899. Later, when this engine was finally found to be a failure, and the writer
constructed the engine in the Institution shops, the starboard transmission shaft
was moved over to the center line and the crank shaft of the engine, which was
carried through on the center line of the transverse frame, was then connected
directly to the imner ends of the transmission shafts.

These shafts, as well as the propeller shafts, were originally constructed
of steel tubing 1.5 inches in diameter and 1/16 of an inch thick, but on account
of the increased power of the large engine it was found necessary to increase
the thickness of the shafts to 4 of an inch. Difficulty was also found with the
tubing of which the shafts were made. This, though not exactly straight when
received from the factory, could be pretty accurately straightened in the lathe
by exercising proper care, but the moment:any real strain was put upon it in
the transmission of power, it again went out of shape and caused serious dam-
age to the bearings by whirling, buckling, and so forth. As the skin of the tub-
ing is really the strongest part, owing to the cold-drawing process to which it
has been subjected, great care was taken to secure shafts which were suffi-
ciently straight for use without machining, but it was finally found impossible
to rely on the unmachined shafts, and all the later shafts for the aerodrome
were made by getting tubing a sixty-fourth of an inch thicker than was eal-
culated to be necessary and turning off this extra metal in a lathe.

Suitable flanges and collars were brazed to the propeller shafts; but, for
convenience in assembling, the flanges by which the main transmission shafts
were connected to the crank shaft of the engine were at first fastened to the
shafts by serew-threads, the threads being in the proper direction to cause the
flanges to jam against the shoulders of the shafts when the engine turned in
its normal direction. This method of fastening, however, caused serious trouble,
owing to the flanges jamming so tight that it became impossible to unscrew
them after they had onee been used in driving the propellers. The usual pro-
visions of keys and key-ways adopted in general engineering practice, where
solid shafts are employed, were, of course, out of the question, since the shaft
would have to be greatly increased in thickness throughout its entire length

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merely to provide the extra metal at the small place in which the key-ways
were formed. Taper pins either sheared off or very soon stretched the holes
so badly as to leave the parts loose, and were otherwise very unsatisfactory.
The method finally adopted, which proved very successful, was that of forming
integral with the couplings shallow internal tongues and grooves which fitted
corresponding tongues and grooves either in the exterior surface of the shafts
or in collars brazed to them at the proper point. The form of flange coupling,
in which bolts draw the two flanges tightly together, was also a source of con-
siderable trouble and delay, which was finally overcome by forming shallow
tongues and grooves in the faces of the flanges, the tongues taking up the tor-
sion and relieving the bolts which held the flanges together of all strain ex-
cept one of slight tension. The same difficulties experienced in mounting the
couplings on the shafts were met with in connection with the gears, both on
the propeller and transmission shafts, and were finally obviated in a manner
similar to that described above.

The bevel gears originally constructed for transmitting the power from
the transmissiéh shafts to the propeller shafts, were made of case-hardened
steel and were eight-pitch, twenty-five teeth, with three-quarter inch width of
face. The gears were very accurately planed to give as perfect a form of
tooth as possible, in order to avoid loss of power in transmission, and although
the manufacturer who cut the teeth on them asserted at the time they were
made that they would not be capable of transmitting more than five horse-
power, yet they actually did transmit considerably more than twelve horse-
power on each set; but they were not strong enough to transmit the full power
of the large engine which was finally used. The gears that were finally used
were similarly constructed of mild steel which was case hardened 1/64 of an
inch deep after they were finished, there being thirty-one teeth in the gear on
the transmission shaft and forty teeth in the one on the propeller shaft, the
teeth being eight-pitch, three-quarters of an inch face. These light gears proved
amply strong, and several times stood the strain which they accidentally re-
ceived when one of the propellers broke while the engine was under full power,
and thus threw the entire fifty horse-power over on the other propeller, which
was consequently driven at a greatly increased speed.

Plain bronze bearings had been used throughout on the model aerodromes,
but in the construction of the large aerodrome ball-bearings were used on all
of the propeller and transmission shafts, not only on account of the decreased
loss through friction, but also because ball-bearings can be built much lighter
than solid bronze ones, and, furthermore, do not present such great difficulties
in lubrication. However, owing to the limited size which it was possible to se-
eure for these bearings, because of their having been originally designed for only
twenty-four horse-power, and without any margin for a later increase of the

178 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

space in which they had to be applied, they were never really large enough
for the work they had to do when transmitting the full power of the large en-
gine. They gave continual trouble, and were the source of delay which, while
it cannot be accurately measured, since there were often other causes, yet might
be conservatively estimated at not less than three or four months. Such a de-
lay, when reckoned in retrospect, can easily be seen to have caused an expense
which would have sufficed for almost any change in the bearings, bed plates,
ete., had the change been made immediately after the bearings were found to
give trouble. With the better steel which it is now possible to obtain for the
races of the bearings, and with the high-grade balls now obtainable, the bear-
ings could be readily replaced without changing any other parts and still be
amply strong for the work.

PROPELLERS

Both the tests on the whirling-table and the actual results with the models
had shown that propellers which were true helices formed out of wood were
rather more efficient than those constructed by the use of a hub in which were
inserted wooden arms, forming a framing over which cloth was tightly drawn.
But the very great difference in the cost of construction and the facility with
which the latter type could be repaired in case of damage—the wooden ones
were practically of no use if once they were much injured—made it seem ad-
visable to construct all the propellers for the large aerodrome in the manner
just explained. Several pair of small propellers had been built on this plan,
some as early as 1895, and one very important advantage had been found to
be possessed by this type besides cheapness and facility of repair. Wooden
propellers of even so small a diameter as one metre had been found to suffer
a quite appreciable bending of the blades, due to the thrust produced by them,
even though the blades had been made of considerable thickness. In planning
a propeller 2.5 metres in diameter for the large aerodrome it was seen that in
order to make the blade sufficiently strong to withstand its own thrust it would
be necessary to make it inordinately thick, which, of course, would mean a con-
siderable increase in weight. In fact, it was seen that the weight of the larger
propellers would increase practically as the cube of the diameter; which, for
the 2.5-metre propeller, would involve a weight of something over fifteen times
the weight of those one metre in diameter. The other type, which for conve-
nience we will call ‘* canvas covered,’’ permitted the bending moment produced
on the blade by the thrust to be taken up by guy-wires running from the cor-
ners of the blades to a central post projecting from the hub of the propeller,

and it was found that in this way a considerable saving in weight could be
effected,

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 179

In November, 1897, in order to obtain by actual test some data on pro-
pellers, such as it was planned to use on the large aerodrome in case it was
later built, it was decided to construct one propeller 2.5 metres in diameter and
1.25-pitch ratio with two blades, each covering the sector of 36 degrees on the
projected circle. About this same time an engine builder, who some years be-
fore had made some experimental model engines in the Institution shops, pro-
posed to construct a gasoline engine for the proposed large aerodrome. As
past experience, not only with such engines but with all other forms of ex-
plosive motors, had not been very reassuring it was thought best to make brake
tests of one of the heavier engines which he was at this time building, and at
the same time make tests with one of these large propellers. A first series of
tests was made at several different speeds, and then a second series was made
with the engine driving the propeller at the same speeds. The engine varied
so much, however, in the power developed at any speed that the data obtained
were of little value. As it was also desired to learn just how much thrust
could be obtained from these propellers, when driven by a given herse-power, a
special hand car was fitted up to carry the engine, which was connected to a
shaft on which the propeller was mounted. The propeller was raised above
the floor of the car and projected over the rear end of it so as to be as little
disturbed as possible by the deflection of the air currents caused by the car.
This car, with the engine and propeller, was tested on a track near Mount Holly,
N. J., in November, 1897, but the results were very unsatisfactory. In the first
place, the car with the engine mounted on it was so very heavy and offered
such a strong tractive resistance that very little speed of propulsion could be
obtained. In the second place, the engine, which was said to have furnished
over six horse-power on Prony-brake tests, evidently did not furnish anything
like this amount of power at this time. And in the third place, the propeller
was evidently far too large to permit the engine to run at the speed at which
it would develop a reasonable amount of power unless some reduction gearing
were interposed between it and the propeller. As the tests, for various reasons,
had to be made at a great distance from Washington, and the supervision of
them had to be entrusted by Mr. Langley to others, who either did not under-
stand or appreciate the value of obtaining accurate data, it was found imprac-
ticable to continue them.

The large propeller used in these tests was built without special regard to
weight, since it was expected that it would be subjected to rather rough usage
under the very sudden strains produced by the irregular working of the gas
engine. Its hub was made of brass tubing, the horns being brazed to rings
which were slid over a central tube, the rings being finally soldered to the tube
after the arms had been adjusted to the positions which would give the blade
the correct shape and dimensions. The wooden arms were 1.5 inches in diam-

180 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. Lyi

eter at the hub end, tapering to 1.25 inches at the end of the blade. The blade
was exceedingly stiff as regards pressure produced by thrust, but it was found
to be considerably strengthened and made very much safer when guy-wires were
added, in the manner explained above. This general type of construction was
adhered to in all the future propellers for the aerodrome, though slight mod-
ifications, both as to the size of the arms and the number and position of the
cross-pieces which formed the framing of the blade, were adopted from time to
time. A pair of heavy propellers, 2.5 metre, 1.25-pitch ratio, 36-degree blade,
the hubs of which were formed of brass castings, was, however, constructed
for experimental purposes, where weight was not an important factor.

When these propellers were designed, the calculations as to their size and
the horse-power which would be required to drive them at a certain speed were
based on the very incomplete data obtained from the various propeller tests
conducted during the preceding years. When later calculations were made for
them, on the data obtained in the more accurate tests made in the summer of
1898, it was found that the power of the engines with which it was proposed to
equip the aerodrome would not be sufficient to drive the propellers at anything
like the speed which the former calculations had shown would be possible; and
that, therefore, either the ratio of the gearing between the propellers and the
engine would have to be changed so as to permit the engine to run at a very
much higher speed than the propellers, or that propellers, having either less
pitch or a smaller diameter, and possibly both, would have to be substituted for
these larger ones.

Since it was easier to change the propellers than to change the gearing,
a new set of propellers was designed which were of 2 metres diameter, with a
pitch ratio of unity, and with a width of blade of only 30 degrees. It was cal-
culated that 20 horse-power would drive these two propellers at a speed of 640
R. P. M., when the aerodrome was flying at a speed of 35 feet per second and
the propellers were slipping about 50 per cent, this bemg found to be about the
speed at which the engines might be expected to develop their maximum power.
As the larger propellers having the brass hubs were thought to be excessively
heavy, the hubs weighing 10.25 pounds each, and as any change either in size,
pitch, or width of blade necessitated a new set of patterns in case the hubs
were cast, it was decided to construct the new hubs of steel tubing. The weight
was further reduced by decreasing the size of the wooden arms to 1} inch in
diameter at the hub, tapering to 1 inch at the end of the blade.

After the engine builder in New York had been unable to fulfil his contract
on the engine, and it had been condemned, propeller tests were made with the
experimental engine built in the Institution shops. These tests showed: First,
that the results which might be expected from larger propellers could be very
safely predicted by extrapolation from the results of the propeller tests of 1898;

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 181

and, second, that in order to get a thrust which would equal fifty per cent of
the flying weight of the aerodrome it would be necessary to use propellers larger
than two metres in diameter unless a very large surplus of power were pro-
vided. It was accordingly decided to make a set of propellers intermediate be-
tween the two-metre, unit-pitch ratio, thirty-degree blade ones, and the original
ones which were two and one-half metres, one and one-quarter-pitch ratio, thirty-
six-degree blade. A set was, therefore, designed two and one-half metres in
diameter, unit-pitch ratio, and thirty-degree width of blade, the hubs being made
of steel tubing brazed up in the same manner as the two-metre ones, and the
wooden arms of the blades being one and three-eighths inches in diameter at the
hub end, and tapering to one inch at the end of the blade.

Later, when the larger engine was actually tested in the frame, the inabil-
ity of the original transmission and propeller shafts to stand the extra strain
caused by the engine starting up very suddenly at times, together with the un-
satisfactoriness of the serew-thread method of fastening the gears and couplings
to the shafts made it necessary to provide new shafts, gears, couplings, ete. It
was then decided to change the ratio of gearing between the engine and the
propellers, which had been one to one, so that the engine might run faster and,
therefore, permit the use of larger propellers. For constructional reasons the
ratio chosen was thirty-one to forty, thus making the engine run approximately
one-third faster than the propellers.

In the various tests made of the engine working in the frame there were
two or three instances in which the propellers were damaged either by the sud-
den starting of the engine or by their not being able to stand the strain to which
they were subjected by the power absorbed, but in every case such breakages
were found to be due to imperfections of the brazing in the joints. While,
therefore, it would have been desirable to make the propellers somewhat heavier,
yet since the total weight of the aerodrome had been growing so very rapidly,
it was felt that this need not be done, as a pair of propellers which had stood
quite severe service in shop tests might reasonably be expected to stand the
strain of actually propelling the aerodrome through the air.

Nevertheless, when in the summer of 1903 the actual trials of the large
aerodrome were started, it was found that the very important difference be-
tween a propeller working in a closed room and one working in the open air
had not been given due consideration. Several sets of propellers, 2.5 metres in
diameter, unit-pitch ratio, 30-degree blade, had been constructed and were on
hand, in order that no delays might be caused through a lack of such extra
parts. On September 9, 1903, when the aerodrome frame without the wings
was mounted on the launching car on top of the boat for some trial runs with
the engine to make sure that everything was again in readiness, before the en-
gine had made 500 revoiutions, the port propeller broke; and a few minutes

182 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

later, when a new propeller had been substituted for this and the engine was
again started up, the starboard propeller also broke. When, upon further trials
and replacements of propellers, all had been so thoroughly demolished that
there was not a complete set remaining, it was seen very clearly that the strains
produced on a propeller working in the open air are very much greater than
those produced in shop tests, where the air is necessarily quiet. These open-
air tests of the propellers had demonstrated that their weakest point was where
the steel tubes which received the wooden arms of the blade terminated, and that
another, though not so serious, point of weakness was where the steel arms
were brazed to the central hub, the thin metal tending to tear loose even before
the brazed joint would give way. It was, therefore, decided to construct im-
mediately a new set of propellers in which the steel arms should be made of
much heavier tubing, that is, a sixteenth of an inch thick at the end where it
was brazed to the central hub, and tapering in thickness to one-thirty-second
of an inch at the other end. These arms were further made twelve inches long
in place of being only three inches long as before. This added length carried
the steel out beyond the point where the first section brace joimed the three
arms together, and where they were further strengthened by having the cloth
covering tightly stretched around them. In order to utilize such of the hubs of
the former propellers as had not been seriously damaged when the propellers
broke, it was also decided to try the effect of merely adding an extra length of
tube to the short arms by means of a thimble slipped over and brazed to the
two parts, which would make these arms twelve inches long. The construction
of these propellers was pushed as rapidly as possible; and after their comple-
tion no further trouble was at any later time caused by insufficient strength
of the propellers. Even in the test of October 7, 1903, when the aerodrome
came down in the water at a speed of something like fifty miles an hour, and
at an angle of approximately forty-five degrees, no break occurred in either
propeller until, when the aerodrome was plunging through the water, a blade
of one propeller was broken by the terrific blow which it received when it struck
the water under the impulse of the engine driving it at full speed. The severity
of this blow is attested by the fact that the shaft, which was of steel tubing one-
eighth inch thick, was twisted about ninety degrees.

This experience with propellers very strongly emphasizes the fact that on
any flying machine the strains which are apt to be met with in the open air must
be allowed for in the proportioning of the parts of the machine. But since an
indiscriminate increase of strength in all the various parts of the machine would
entail a prohibitory weight, very careful judgment, based on experience, will
have to be exercised in deciding just where added strength must be employed,
and also where the ‘‘ live strains ’’ are not apt to exceed very appreciably the
calculation for statical conditions.

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 183

Owing to Mr. Langley’s belief that the tests of the man-carrying aero-
drome must not only be made over the water, but that it was necessary that the
machine be launched from a car running on a track at a considerable elevation
in order to permit the machine to drop a short distance after being launched in
case it was not quite up to soaring speed when launched, it was necessary that
the aerodrome be so constructed that it could be readily transported to the
launching track from the interior of the house-boat where it was stored. This
plan of storing the main body of the machine in the interior of the boat and
hoisting it to the launching track just before attempting a flight (some of the
difficulties of which may be more clearly appreciated by an inspection of Plate
60), made it necessary that the wings, tail and guy-posts be so constructed as to
be readily attachable to and detachable from the main frame, and since the
weather conditions are seldom suitable for a test for more than a couple of hours
at a time, it was necessary that the mechanism employed for attaching these
parts be so arranged that the proper settings of the different parts could be
quickly obtained, and without requiring the exercise of judgment which past ex-
perience had shown did not often manifest itself during the hurry of the prepa-
rations for a test. While the wings, therefore, were made removable, yet all of
the sockets, guy-wires, etc., which were loosened in removing them, were made
with positive stops on them so that each fitting that was to be tightened up
in assembling could be adjusted to its definitely determined position.

As all of the models had been constructed with these same parts removable
in order to permit them to be readily shipped back and forth in the many trips
which had been made with them from Washington to Chopawamsic Island, the
same details of arrangement were used for attaching these parts on the large
aerodrome, though the actual fittings by which the parts were attached in the
latter case became more elaborate.

In the drawings, Plates 52, 53 and 54, the method of attaching the wings
to the frame is clearly shown. Each of the two main ribs of each wing
was secured to the midrod of the frame by a wing clamp, shown in detail in
Figs. 1, 2,5, 6 and 7 of Plate 59. Figs. 1 and 2 show the clamp for the middle
main rib of each pair of wings, and Figs. 5 and 6 show the clamp for the main
front rib, the latter being so constructed that the wings could be rocked on the
midrib clamp as a pivot and secured at any angle of lift desired from 64 de-
grees to 15 degrees. The horns on each clamp merely acted as receiving sockets
for the ends of the ribs, and were not in any way intended to do anything
more than merely hold the ends of the ribs in their correct positions. The wings
were fastened to the frame by the guy-wires which ran from two points on each
main rib to an upper and a lower guy-post mounted on the midrod. The sys-
tem of guy-wires for the wings is clearly shown in Plates 52, 53 and 54, and

184 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

in Plate 61, which shows the aerodrome mounted on its launching car at the
rear end of the track, and with the front pair of wings in place and all the
euy-wires adjusted. The details of the guy-posts are shown in Plate 62, where
it will be noted that the lower guy-post was of wood, with metal fittings, and
was 2 metres long from the center of the midrod to the bottom, while the
upper guy-post was a steel tube 109 centimetres long from the center of the
midrod to its top. The guy-wires from the middle rib of each of the pair of
wings were fastened to the fittings at the bottom of the lower guy-post, while
the wires from the front main rib were fastened to the fittings which were
brazed and riveted to the slidable collar, which was mounted on the steel tube
forming the cap on this guy-post. This collar was made slidable to permit the
angle of lift of the wings to be readily changed without affecting the length of
the guy-wires. This collar, when once set for any particular angle of the wing,
was prevented from sliding by a taper pin (not shown) which passed through
it and the guy-post. In order to secure the wings more rigidly to the main
frame and thereby throw on it all torsional strains from the wings, which it
was specially designed to take, each of the middle main ribs was secured to
one of the main tubes of the main frame by an auxiliary clamp at the point
where this rib crossed the main tube. These auxiliary clamps are clearly shown
in Figs. 3 and 4 of Plate 59.

Projecting from the lower end of each of the lower guy-posts was a five-
sixteenth-inch steel rod about one inch long, as clearly seen in Plate 62. Brazed
to the side of this rod, in such a position that it would project towards the rear
of the aerodrome when the guy-post was in position, was a small arm or bracket.
When the guy-post was in place with the aerodrome on the launching car,
this pin was in a slot formed in a metal cap on the top of the small folding
upright at the front or rear of the car, as seen in Fig. 1, Plate 63, while
Fig. 2 of Plate 63 shows the pin just being inserted into this slot as the
euy-wires of the guy-post are being fastened. This small arm or bracket on
this rod projected under the cap to prevent the rod of the guy-post from be-
ing lifted out of the slot in the folding upright, when the wind acting under
the wings tended to lift the aerodrome from the car. Particular attention is here
‘alled to this apparently insignificant detail, for it was this arm or bracket on
this small rod of the front guy-post which, hanging in the cap on top of the
folding upright, caused the accident in the launching of the aerodrome on Octo-
ber 7, 1903. Gertain it is that but for the accident due to this apparently in-
sionifieant detail, success would have crowned the efforts of Mr. Langley, who
above all men deserved success in this field of work, which his labors had so

greatly enriched.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

20

Fie. 3

HOISTING AERODROME TO LAUNCHING-TRACK

VOL. 27, NO. 3, PL. 60

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VOL,

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

GUY-POST AND PIN ON LAUNCHING CAR

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no. 3 LANGLUY MEMOIR ON MECHANICAL FLIGHT 185

Aviator’s Car

In determining on a suitable car for the aviator various designs were made,
differing all the way from that in which the aviator occupied a sitting position
facing directly ahead and with practically no freedom of movement, but was
even strapped to the machine to avoid the possibility of being thrown out, to
the one finally adopted, in which he was provided with the greatest freedom of
movement, could either stand or sit, as the occasion seemed to demand, and
could face in any direction for giving proper attention to any of the multitudi-
nous things which might at any time require his attention, and could, if agile,
even climb from the extreme front of the machine to the rear. The wisdom
of giving the aviator complete freedom without hampering him in any way by
provisions for preventing his being thrown out of the machine was amply jus-
tified, as will later be seen in the description of the tests of the machine, where
freedom of movement and agility prevented a fatal accident.

The aviator’s car. was therefore designed to occupy the entire available
space between the engine and the front bearing points, and between the two
main tubes of: the main frame, thus allowing him a space of something like
three feet by five feet. The car itself was shaped like a flat-bottomed boat,
the bottom being approximately level with the bottom of the lower pyramid.
It had a guard rail of steel tubing eighteen inches above the floor, with a cloth
covering drawn over the frame to decrease the head resistance of the appurte-
nances of the engine which were placed at the rear end of the car. The car
was supported by vertical wires passing from its bottom up to the main frame,
and was prevented from longitudinal or side motion by being fastened at the
front to the cross-rod connecting the front bearing points, and at the rear to
the lower pyramid. A light wooden seat extended fore and aft of the car at
a height of about two feet from the floor, this seat resting on blocks of sponge
rubber to absorb some of the tremor which existed in the whole aerodrome
when the engine and propellers were working at high speed. The aviator was
thus free to stand, to sit sidewise or to straddle the seat, and while the network
of wires surrounding him prevented any great possibility of his being thrown
out, yet there was a comparatively large opening between the guy-wires pass-
ing overhead which permitted him to climb out of the machine.

In order to enable the aviator to know exactly how the engine was operat-
ing, a tachometer, giving instantaneous readings of the number of revolutions,
was connected by a suitable gear to one of the transmission shafts and placed
where it could readily be seen.

During 1898 and 1899 considerable time and attention had been given to
designing an instrument to be carried by the aerodrome which would automat-
ieally record the number of revolutions of the engine, the velocity and direction

21

186 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

of the wind relative to the machine, the height of the aerodrome as shown by
a specially sensitive aneroid barometer, and the angle of the machine with the
horizontal plane of the earth. The construction of this instrument was under-
taken by a noted firm of instrument makers, but after many months of delay,
during which it was several times delivered as being complete, only to be re-
turned for further work, it was finally condemned as unsatisfactory, and it was
decided not to encumber the machine with such a delicate apparatus, which,
even if perfectly made, could not be depended on to work properly when mounted
on the aerodrome frame, in which there was a constant, though minute, tremor
due to the high speed and power of the engine.

The completed frame, which is perhaps best shown in Plates 49, 50 and 51,
and Plate 60, Figs. 1, 2 and 3, in spite of its size gave an appearance of grace
and strength which is inadequately represented in the photographs. In making
the designs for the large aerodrome no data were available for use in cal-
culating the strains that would come on the different parts of the frame while
in the air, and the size and thickness of the tubes and the strength of the guy-
wires were consequently determined almost entirely by ‘‘ rule of thumb,’’ backed
by experience with the models. Although the dimensions, shape, and arrange-
ment of most of the auxiliary parts of the machine were considerably changed
during the course of construction in accordance with the indications of the ex-
haustive series of shop tests, the fundamental features of the construction were
practically unaltered, but the changes in the guy-wire system and in the fittings
by which they were attached, made the frame as a whole several times as
strong as it was originally, and it was felt that the direction of further improve-
ments in it would be shown only by actual test of it in flight where any weak-
nesses would be certain to manifest themselves.

It may be well to remark here that even with the data which were later ob-
tained, judgment based on experience proved after all to be the safest guide for
proportioning the strength of the various parts. It can be assumed that a live
stress will produce a strain ten times as great as that due to a static stress on
the part when the machine is stationary. For greater safety, it would be still
better to assume a strain twenty times as great. If one is building bridges,
houses, and similar structures, where weight is not a prime consideration, it
would be criminal negligence to fail to provide a sufficient ‘‘ factor of safety,”’
or what in many instances may be more properly termed a ‘‘ factor of igno-
rance,’’ while at the present time the insistence on large factors of safety in
machines intended to fly would so enormously increase the weight that, before
one-half the necessary parts were provided, the weight would be many times
what could possibly be supported in the air. Later, no doubt, as experience is
gained in properly handling the machine in the air, increased strength entail-

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 187

ing increased weight may be added in proportion to the skill acquired; and there
is no doubt that man will acquire this skill with marvelous rapidity, approach-
ing, if not equaling, that exhibited by him in the use of the bicycle, which,
when first ridden, requires not only all of the rider’s skill but that of a couple
of assistants, but when once mastered requires hardly more thought for its
proper manipulation than even the act of walking involves, the balancing and
guiding being done intuitively merely by the motion of the body and with prac-
tically no exertion.

CHAPTER VI
CONSTRUCTION OF SUPPORTING SURFACES

_An examination of the wings of birds, whether those of soarers or of any
other type, impresses one not only with the general strength of the wing, but
also with the fact that, while it possesses considerable stiffness, there is also a
graduated pliability, not only of the whole wing, including the bones, but more
especially in the feathers, the rear tips being exceedingly pliable so that, when
the wing is held in a stiff breeze, they are seen to be easily deflected in a gentle
curve towards the rear and upper side. This lack of rigidity has several ad-
vantages, among the more notable of which is the lessening of the strains on
the wing caused by sudden wind gusts. Of great importance is the further fact
that a supporting surface having a graduated pliability, such as is possessed
by a bird’s wing, does not experience a shifting of the center of pressure to
the same extent as a rigid surface of similar form. Furthermore, since any
bird, even the best soarer, must use its wings not only for soaring, but, when
starting to fly from a state of rest, for flapping, a rigid surface would not
furnish anything like the same universally available sustaining and propelling
means that the bird’s wing does. ,

In an inspection of the various wings or supporting surfaces which Mr.
Langley built, from the very earliest rubber-pull models up to the successful
steam machines Nos. 5 and 6, the point which is most impressed upon the ob-
server is the increasing strength and rigidity embodied in these wings. While
the success with the later models was due to many things, including the devel-
opment of a strong frame and a suitable power plant giving sufficient power
for the permissible weight, besides the very important development of effec-
tive equilibrium mechanism, yet it is safe to say that even with the development
of all these other things to the state to which they had been brought in 1896,
suecess would not have been achieved had not the wings themselves been simul-
taneously changed from the very flimsy construction which was at first used to the
later type, using a very strong and rigid wooden frame over which the cloth cover-
ing was tightly stretched, and which possessed only a small amount of pliability
at the extreme rear ends of the cross-ribs.

The development of this successful type of wing for the models, it will be
remembered, had been achieved only after an extensive series of experiments;
and it was realized that the construction of suitable wings for the large aero-
drome, even with the knowledge gained in the early work, would be still more

1858

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 189

difficult. The problem was that of constructing for a very little greater weight
per square foot, wings containing approximately sixteen times the area of the
model wings.

It will be recalled from the previous description of mode] Aerodrome No.
5, that its four wings had a combined area of 68 square feet and weighed ap-
proximately 2500 grammes, or 37 grammes per square foot. It was not ex-
pected that the large wings would be of so light a weight per square foot,
which would have meant only about 35,500 grammes (approximately 78 pounds)
weight for the 960 square feet originally planned. It was hoped, however, that
the increase in weight per square foot for the large wings would be less than
the square root of the increased linear dimensions. In this case, the increase
in linear dimensions being approximately four, it was, therefore, hoped that
the larger wings would not have quite twice the weight per square foot of the
smaller ones; the computed weight permissible for the large wings was there-
fore placed at 120 pounds.

To obtain the required area within the permissible limits of weight two
well-defined paths of procedure were open: First, it was possible to so modify
the structural form of the wing as to obtain the advantage of the increased
strength of trussed structures, that is, by superposing the wings. Or, second,
the ‘‘ single-tier ’’ type of wing, the efficiency of which had been fairly well de-
termined, could be retained, and strength gained without increase of weight by
improving the method of constructing the wooden framework and by extend-
ing the system of guy-wires.

Some knowledge of the superposed type of supporting surfaces had already
been gained by the experiments at Allegheny and the tests of the rubber-driven
models, in which superposed wings had frequently been used; but it was felt
that this knowledge was altogether inadequate to aid in determining either
whether the superposed type of construction possessed in practice the advan-
tages which theory would indicate, or how and at what distance apart the sur-_
faces should be superposed to obtain the best results. In order to obtain the
desired information, a series of tests on the whirling-table of complete wings
suitable for use on the models was made. These experiments were supplemented
by the practical tests with the models, which have already been deseribed in
Chapter III, in order to give the wings a trial under the conditions of flight,
where they would be subjected to the action of the propellers and the uneven
character of the wind.

In addition to determining what type of construction and what form of
surface would give the greatest ‘lift ’’ with the smallest ‘‘ drift,”” these whirl-
ing-table tests supplied data as to how much greater the actual resistance of
the wing with its necessary guy-posts and guy-wires was than the theoretical
resistance, found by extrapolation from the results obtained in the tests of rigid

190 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

curved surfaces formed of wood. The first of this series of tests, the results
of which are given below, was made November 30, 1898, on the superposed wing
shown in Plate 37, Figs. 1 and 2. It should be noted, however, that when this test
was made the wing was not provided with the stiffening strips or the vertical
partitions.

Weight of wing = 1000 grammes; weight of guy- -posts, ete., = 475 grammes; distance of mean
center of gravity of guy-posts, etc., from pivots of balance arm — one- half distance of OP of wing
from pivots of balance arm; the wing, therefore, had a lever arm of two to one with reference to
weight of guy-posts, etc., so that the equivalent weight of guy-posts, etc., = 237 grammes. This gives

1237 grammes of equivalent load on the wing = 2.73 pounds. Area of wing — 21.85 square feet.
@heretors load on wing = 0.125 pounds per square eitoot.

Calculated
Talnaity Me soaring
Angle of en Voeese os yee Drift Drift ST Pest 5
chord, table: (ft BS ae second). (grammes). (pounds). per nee: pounds per
(ft. per 2
20% 10.75 1086 18.1 255 0.561 10.15 36.2
3.02 10.0 1010 16.85 255 0.561 9.47 33.7
5.0° O85) 960 16.0 255 0.561 8.98 32.0
10.0° 7.75 783 13.0 255 0.561 7.3 26.0

The very interesting phenomenon was noted in this test that the ‘* drift ”’
or resistance of the wing seemed to remain unchanged at soaring speed at dif-
ferent angles of elevation. It is hardly probable that this result is accurate,
for the ‘‘ balance arm ’’ undoubtedly twisted under the action of the wing, and
this caused it to strain on its pivots, and thus, to a certain extent, falsify the
record as to drift.

A test of a single-tier wing at difterent angles of elevation was made
on December 6, 1898. This wing was nearly the same as those used in actual
flights of Aerodromes Nos. 5 and 6 in May and November, 1896, the wing be-
ing of the same width fore and aft, but somewhat shorter. The actual wing
was a little too long to permit its being used on the whirling-table in the lim-
ited space of the shop.

Weight of wing = 420 grammes; weight of guy-posts, etc., = 320 grammes; equivalent weight of

guy-posts, ete., = 150 grammes applied on the wing. Therefore, total load on wing = 570 grammes,
Area of wing = 11.2 square feet; equivalent load on wing = 0.112 pounds per square foot.

Calculated
: tang Velocity of ra en Foot- soar ing
Angle of Be aue center of Yeo Drift Drift pounds ape: 5
chord, , wing (grammes). (pounds). per sec.
table. (ft. per min.). second). RV. DOU rine Yr
(ft. per sec.).
2.0° 11.6 1195 19.9 210 0.462 9.2 42.1
3:02 9.75 1005 16.7 157 0.345 5.77 35.3
5.0° 8.25 850 14.2 133 0.293 4.16 30.0
10.0° 6.75 695 11.6 129 0.284 3.29 24.5
12:52 6.0 618 10.3 129 0.284 2.92 21.8

Tn this test it is to be noted that the ‘ drift,’’? or resistance, while consid-
erably greater at soaring speed for 2 degrees than for 5 degrees, remains prac-
ically the same between 5 degrees and 123 degrees. Comparing it with the

preceding test with the superposed wing, it is seen that at soaring speed at an

angle of 10 degrees, the single-tier wing having a load of 0.112 pounds per

Vio Cy 289? were

ad Sera VF

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 191

square foot, has only 129 grammes drift, while the superposed one, while

‘supporting 0.125 pounds per square foot, has 255 grammes drift. More-

over, the soaring speed of the single-tier wing is only 11.6 feet per second,
while the superposed one requires a speed of 15 feet per second.

As the superposed wing tested on November 30 was so weak structurally
that it could not be made to keep its proper shape without adding an excessive
number of guy-wires, it was decided that it was not adapted for use on the
aerodrome, but before abandoning it the partitions and strips were added and it
was again tested on the whirling-table on March 1, 1899, with the following
results:

Weight of wing = 905 grammes; weight of guy-posts, ete., = 320 grammes; equivalent weight of
guy-posts, ete., — 150 grammes applied at CP of the wing; equivalent load on the wing = 1055

grammes = 2.321 pounds; area of wing — 21.85 square feet; equivalent load on wing = 0.1062

pounds per square foot.
Calculated

. - soaring
Angle of Eee One Peieror ve ne Drift Drift nonnde aes 0.5
chord. table. (rt, Penn ) second). ‘&tammes). (pounds.). re eat pounds per
o)e = 8q. .
(fepornce)!
B02 10.875 1100 18.35 250 0.55 10.1 39.81
9.0° 10.75 1085 18.07 250 0.55 9.94 39.19
b0e 10.75 1085 18.07 250 55 9.94 39.19
10.0° 8.0 808 13.47 250 7.4 29.226
10.0° 8.0 808 13.47 250 7.4 29.226
L9tb > 7.875 797 13.8 250 7.32 28.86
10:52 7.875 797 13.3 250 0.55 1.32 28.86
13.0° 7.0 707 11.78 250 0.55 6.48 25.553

An examination of the data obtained in this test shows the wing to be of
slightly less efficiency than when first tested. While it was considerably stronger
it was still too weak for use on the aerodromes.

A second type of superposed wing, Plates 64 and 65, was therefore con-
structed and tested on the whirling-table on March 2, 1899, with the following

results:

Weight of wing = 1025 grammes; weight of guy-posts, etc., — 320 grammes; equivalent weight of
guy-posts, ete., = 150 grammes applied at OP of the wing; equivalent load on wing = 1175 grammes
= 2.585 pounds; area of wing — 21.85 square feet; equivalent load on wing = .1183 pounds per square

foot.
Calculated

Revolutions Velocity of volocity - ; Foot. apeeds
Angle of ae ane center of (ft. per Drift ; et pounus carrying 0.6
chord. table: Sete second): (grammes). (pounds). pera c. pounds per
ale i]. i.
(it per sec.).
502 11.625 1170 19.5 250 10.72 40.087
5.0° 11.625 1170 19.5 250 10.72 40.087
8.0° 10.5 1060 17.7 250 9.75 36.37
10.0° 9.125 919 15.3 250 8.43 31.4
10.0° 9.125 919 15.3 250 8.43 31.4

During the tests on the whirling-table this type of construction seemed to
be exceedingly strong and stiff, and to be easily maintained in whatever posi-
tion it was placed. It was therefore thought that it would prove strong enough
for the aerodrome, and it was accordingly inverted and given a ‘‘ sanding test ”’

192 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vot. 27

by sprinkling sand uniformly over it to such a thickness as to cause it to have
a load of 0.75 pounds per square foot. As it showed no serious deflection or
change of form under the sanding test, it was decided that it was strong enough
for use in tests of the model aerodromes in actual flight.

Upon the completion of these whirling-table tests, the cloth covering of this
wing was painted with collodion varnish, which increased the weight of the
wing only 50 grammes. In order to make the results of its tests more easily
comparable with those obtained before varnishing, the cross guy-wires on the
wing were changed to a slightly smaller size in order to make the weight of
the wing the same-as before. It was tested on March 3, and the following re-
sults were obtained:

Weight of wing = 1025 grammes; weight of guy posts, ete., —= 320 grammes; equivalent weight of
guy-posts, ete., = 150 grammes applied at CP of the wing; equivalent load on wing = 1175 grammes
= 2.585 pounds; area of wing = 21.85 square feet; equivalent load on wing — .1183 pounds per
square foot.

Calculated
= “ 3 soaring
Angioiot =a evoneeigns enone ess Drift Drift Pa reas
chord. table. Tera second). (grammes). (pounds). foe Bee: pounds per
(ft. per sec.),
5.0° 10.5 1060 ert 250 0.55 9.75 36.37
50° 10.5 1060 aly etd 250 0.55 9.75 36.37
10.0° 8.5 859 14.3 250 0.55 7.88 29.4
10.0° 8.5 859 14.3 250 0.55 7.88 29.4

Although the varnishing of the wing seemed to have no effect on the ‘‘ drift,”’
the soaring speed was slightly decreased.

As a result of these tests it was decided to construct three more wings like
this second type, the four forming a complete set for use on the steam-driven
models Nos. 5 and 6. Although the tests on the whirling-table indicated a su-
perior efficiency for the ‘ single-tier ’’ wings, and it was not expected that in
actual use on the aerodrome the result would be different, yet it was felt that
as the conditions of actual use are so very different from those of a whirling-
table experiment it would not be safe to decide too definitely against the su-
perposed wings without first giving them a test under actual conditions. Aside
from the decreased lifting effect shown by the superposed wing when com-
pared with the ‘‘ single-tier ’’ one, it was also thought that under the actual con-
ditions of use on the machine the superposed wing would show up still worse.
The deflection of the air by the front wings diminishes the lift of the rear ones
even for the ‘‘ single-tier ’’ type, and this, it seemed certain, would be greatly
aggravated in the case of the superposed type.

In order to emphasize more fully the results of these tests the following
table is added, which gives the data for the ‘‘ single-tier ’’ wing and this sec-
ond type of superposed one, when each was tested at ten degrees angle of
elevation:

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 64

EXPERIMENTAL TYPE OF SUPERPOSED WINGS, MARCH 2, 1899

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 193

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P e z as ow oO 45 ays o

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RASIN PTO GLOM ah eisersalcrnelss «sic ¢ 4.27 11.2 1.26 10° 11.6 112 025 24.5
Superposed. Type No. 2..... 4.27 21.9 2.59 10 14.3 118 026 29.4

The ‘‘ single-tier ’? wings actually used on Aerodrome No. 6 were 5.33 feet
long, while the wing tested above was only 4.27 feet long. In order to bring out
more fully what might be expected of Aerodrome No. 6, when using the two
different types of wings, the following table, calculated from the preceding
one, is given. This shows the results which might be expected from the aero-
drome when the resistance of the machine itself was included:

Aerodrome No. 6 without wings weighs 22 pounds.
=~ Og a Le} !
Secs Seo chon Geese voy se ae 88 anon
a Bao 206 BOPa PES CS secs og Mn peg AOG
I CSo ADS Bbq 190m pati = (ees oe AO BHO oD
to gon wf woe gota Hnsety GY Ba soo “en
&§ $ha See Seek S2ky EA BeES So gs Hee eee
A <482 ESS E353 G88h ARdSSS eS as HSA AAS,

“ Single-tier ” (short).... 4.27 44.8 5.04 27.04 0.603 6.06 1.0 7.06 27.0 0.35 .70

.“ Single-tier ” (full length) 5.30 54.0 5:5 27.5 0.51 6.18 1.0 7.13 24.7 0.32 .64

Superposed. Type No. 2. 4.27 87.6 10.36 32.36 0.369 69 1.0 7.9 25.3 0.364 .73

The first line shows the calculations for the aerodrome when equipped with
the short ‘‘ single-tier ’’ wings; the second line, when equipped with the ‘‘ single-
tier’? wings of the full length used in the flights of 1896; and the third line,
when equipped with superposed wings, Type No. 2.

It will be seen that, on the whole, the result of the comparison of the full-
length ‘‘ single-tier ’’ wing and the superposed one is less in favor of the latter
than was to be expected, as, aside from its greater structural strength, it seems
to have no real point of superiority, except that it is shorter; and, as already
pointed out, one point of presumable inferiority, though not exhibited in the
table, is the fact that the rear set of wings would suffer relatively more from
being in the lee of the front ones, in the case of the superposed wings, than in
the case of the ‘‘ single-tier ’’ ones.

Besides these ‘‘ conventional ’’ forms of wings, various other types were
tested on the whirling-table. The data of these tests are not given, as in the
rough preliminary tests the results were so entirely negative in character that
accurate quantitative tests were never made. However, since in work of this
kind the greatest delay is experienced in learning what not to do, and in rid-
ding one’s self of freak notions which are continually suggesting themselves, it
may be well here to describe sufficiently at least one of these types of wing to
enable others to avoid any loss of time in experiments with it. Since the prin-
cipal disadvantages of a wing possessing considerable width in the fore and
aft direction are due tc the great extent through which the center of pressure

194 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

shifts when the velocity of advance or angle of incidence is changed, and to the
further fact that a wide surface does not support proportionately as much per
square foot as a long and narrow one, it was thought that some advantage
might be gained by making the covering of the wing in the form of strips,
the edges of which would be perpendicular to the direction of motion, or by
making this covering in more or less slat-like form, which would permit the air
which had already been acted upon by the leading slat to slp through between
the rear edge of the first slat and the leading edge of the succeeding one. In
the tests on the whirling-table, however, it was found that this type of construc-
tion not only did not possess any advantages, but was even less effective than
a similar one in which the covering was continuous. The difference was prob-
ably due to the fact that the air which passed between the slats reduced the
suction on the upper side of the following slat, and also to the fact that the
distance between the slats was not sufficient to gain the effect of having each slat
act on air which had not already been partially deflected by the preceding one.

In view of the results of these tests on various types of wings, it was de-
cided that in constructing the first set of wings for the large aerodrome it would
be best to employ the ‘ single-tier ’’ type, which had proved successful with
the models, and that after getting a successful flight with these the super-
posed wings would be tried in order to get, if possible, the advantage which
they possessed of being structurally stronger and more compact. It was there-
fore clear that any gain in the strength and rigidity of the first set of wings,
as a whole, would have to be obtained by improvements in the construction of its
integral parts, that is, in the main and cross-ribs which made up its framework.

Before attempting to proportion the parts of the necessary wooden wing
frame, which it was expected would probably undergo many changes before
a final design was secured which would embody maximum strength for min-
imum weight, various tests were made to determine just how light a cloth cov-
ering could be obtained which would be strong enough and sufficiently im-
pervious to the air. In the construction of the wings for the models a good
grade of China silk had been employed, but on account of the greatly increased
quantity of cloth required for the large wings, it was hoped that something
approximately as good as the silk could be secured at a much less cost, and
rarious grades of percaline were therefore tested. The weight of the various
erades of percaline ranged from three grammes to ten grammes per square
foot, the lighter samples being of a rather coarse mesh, while the heaviest
ones were not only close mesh but some specimens contained a large amount
of ‘ sizing.’? The particular grade which was finally adopted weighed seven
erammes per square foot. This material was practically impervious to air at

a pressure of one pound per square foot, which, of course, was considerably

se

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 195

more than it would be subjected to in flight. This grade of perealine weighed
approximately one and a half times as much as a grade of silk, which on test
was found to have a slightly greater tensile strength than the perealine, though
the latter did not ‘‘ flute ’’ or ‘‘ pocket ’’ nearly as much as the silk. More-
over, the cost of the percaline was only about one-third that of the silk, and
it was chiefly for this reason that percaline was adopted in place of silk. <Al-
lowing for necessary seams and extra material to be turned over at the front
and rear edges of the wings, the percaline covering, which under the original
plans comprised approximately 1000 square feet, was therefore calculated to
weigh approximately 7000 grammes, exclusive of the necessary cords for lacing
the coverings to the wooden frames of the wings.

As the one hundred and twenty pounds allowed for the four wings per-
mitted only thirty pounds per wing, and as the cloth covering, lacing cords,
ete., were found to weigh something over four pounds, there remained only
about 25 pounds as the permissible weight of the wooden framing, including
the necessary metal clips, secondary guy-wires, ete., for each wing. With the
relative proportions of the various parts of the wooden framing of the wings
of the models as a basis, it was decided to make the main ribs of the large
wings 1.5 inches in diameter for one-half their length, and have them taper from
this size to one inch in diameter at the extreme point. After making allow-
ance for the weight of these ribs, it was found that, if the cross-ribs were to
be spaced no farther than ten inches apart, and the two end ones were to be
made at least as wide as 1.5 inches in order to resist the end strain due to the
stress of the cloth, the twenty-six intermediate cross-ribs could be only seven-
sixteenths of an inch in diameter at the point where they crossed the main rib,
and that they must be tapered to three-eighths of an inch in diameter at the
front end and to one-fourth of an inch in diameter at the rear tip.

A trial wing, whose total weight was 30 pounds 2 ounces, was made up with
the various parts of its frame of the above dimensions. Even upon inspection
it appeared to be too flimsy to withstand the sudden gusts of wind which were
certain to be met in actual practice. In order, however, to get some definite
data as a guide, the wing was inverted and guyed in the same way that it was
proposed to guy it on the aerodrome, and a uniform thickness of sand was then
sprinkled over it to such a depth as to give it a load of 0.7 pounds per square
foot. Even before one-quarter of the sand was sprinkled over it, it was seen
that the wing was rapidly going out of shape, and it was feared that the full
amount of sand would not only seriously distort it, but would even break it.
The full quantity of sand, however, did not break it, but distorted it to such
an extent that, had the pressure been due to its being propelled through the

air, its serious change in form would have rendered it worse than useless.

196 : SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE Vor: 2

While the main ribs had shown a certain amount of deflection under the sand-
ing test, the more serious distortion had been in the cross-ribs, the small guy-
wires, which had been fastened to each cross-rib, becoming loose instead of
tight, as had been expected, since the rib tended to increase its curvature in-
stead of straightening out. This increase in the curvature of the cross-ribs
was partly overcome by tying the guy-wire flat against the cross-rib for a dis-
tance of about 2 feet from the rear tip. But while this caused the guy-wire to
tighten the general contour of the wing showed very little improvement, as
the ribs now assumed a curve more or less like the letter S, the rear tip now
being bent downward to form the tail of the elongated S.

From this sanding test it was seen that the cross-ribs must be materially
stiffer, and a new set was accordingly made one-sixteenth of an inch larger in
diameter at the various points of measurement. Upon giving the wing, equipped
with these larger ribs, a sanding test it was found that, while there had been
some improvement, it was entirely too flimsy, even when it had been double-
guyed by running a second wire on each cross-rib from the middle of the por-
tion in front of the mid-rib to the middle of the portion behind the mid-rib.
As the weight of the wing with these larger solid cross-ribs had now increased
to more than 33 pounds, and the wing had proved itself altogether too weak
for use on the aerodrome, it was evident that some other plan of constructing
the ribs which would give greater strength for the same weight must be found.
At first sight it might appear that the obvious way of increasing the stiffness
of the cross-ribs was to employ a cross-section other than a round one, since
material added to the depth of the rib is very much more effective than if
added to the width. It must, however, be remembered that these cross-ribs
were 11 feet long, and that, as the main mid-rib was 6 feet in front of the
rear tips of the cross-ribs, with no intermediate bracing, except the light threads
by which the cloth cover was attached, it was inevitable that, should the depth
be made materially greater than the width, the rib would buckle sideways.
Test ribs of L-beam form, which are later described, were constructed, but, al-
though they proved exceedingly stiff, had to be discarded.

In view of these facts the obvious remedy appeared to be to make the rib
hollow, and one cross-rib, % of an inch in diameter at the point where it crossed

5

the main rib, tapering to % of an inch at the front and 2 of an inch at the rear
tip, was accordingly constructed. Tests showed that this form of rib, which
was about 10 grammes lighter than the }-inch solid ribs, was much stiffer than
anything yet constructed. But when a wing, with cross-ribs of this size placed
20 inches apart, was sanded it was found that, although a great advance in
construction had been made, still further improvement was necessary before a

suitable wing for the large aerodrome could be procured.

pitied

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 197

Before proceeding with the construction of any more complete wings, an
extended series of experiments was made in order to secure ribs of proper light-
ness and strength. Various forms of metal tubes were tested; but, although
aluminum seemed at one time to promise good results, it was found that hol-
low ribs could be constructed of spruce which were much stronger than aluminum
tubes of the same weight. In order to determine more accurately what mode
of construction would give the greatest stiffness and strength for a minimum
weight, it was decided to make up some test pieces of different forms before
making up complete ribs. For convenience in construction, these test pieces
were made straight and shorter than the large cross-ribs. Hach piece was
tested by fastening it in the testing clamp with 1 metre of its length projecting
horizontally, and attaching at its end a weight of 1 kilogramme. The deflec-
tion from the horizontal gave an index of the stiffness of the piece under
examination.

The first test piece was a hollow square, 17 mm. length of side on the ex-
terior, and 11mm. length of side on the interior, the walls thus being 3mm.
thick. This weighed 73 grammes per metre and had small internal stiffening
pieces, like the partitions in bamboo, glued into it 4 inches apart. A weight of
1 kilogramme at the distance of 1 metre gave a deflection of 56mm. The sec-
ond test piece was a duplicate of the first one, except that it had no internal

(a)

stiffening pieces, and the weight per metre was made the same, 73 grammes, as

formerly, by leaving the walls a fraction thicker. The deflection in this case
- v? 2 c=)

was, as would be expected, exactly the same as in the first one. The first test
piece, however, was superior to the second one in that it was stiffer against be-
ing crushed in by accident. The third test piece was a hollow cylinder, 22 mm.
outside diameter and 17 mm. inside diameter, the walls thus being 2.5mm. thick,
The weight per metre was 91 grammes, and the deflection was 46mm. The
fourth test was made by taking two of the original solid cross-ribs, 12 mm. in
diameter, and fastening them in the clamp side by side, with a length of 1 metre
projecting. The weight per metre for the two ribs was 105 grammes, and the
deflection produced on the two by 1 kilogramme at 1 metre distance was 115 mm.
The fifth test piece was an I-beam of spruce, having a depth of 25mm., with
the flanges 12.5 mm. wide and the web 3mm. thick. The weight per metre was
65 grammes, and the deflection was 26mm. All of these test pieces were made
of carefully selected straight-grained spruce.

It is readily seen that the test piece having the beam section weighed less
than the hollow square in the first and second tests, and had a deflection of less
than half. This Lbeam section, however, did not show up so well when a longer
piece was tested, for as soon as the leneth was made appreciably greater than
a metre it began to twist, the twisting becoming more and more serious the

198 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

greater the length, until with a piece 11 feet long, the full length of a cross-
rib, the twisting was so serious as to make the rib practically useless. It was
at first thought that this twisting might be overcome by making the webs slightly
wider, and it would to a certain extent, but in looking ahead and planning how
the cross-ribs were to be fastened to the main ribs, the Lbeam section was seen
to present so many difficulties that it was thought hardly worth while to spend
time on further experiments with it. This decision was made all the more im-
perative by foreseeing the difficulty of bending the I-beam section to the curve
which the cross-ribs were to have. In fact it had been found by experience
that while many different forms of ribs could be bent to the proper curve by
steaming and clamping them over a form and then drying them out while still
clamped to the form, yet the grain of the wood varied so in different ribs, that
of a dozen steamed and bent over the same form it was seldom that as many
as three would have approximately the same amount of curvature when re-
moved from the form after drying. If, however, the curve was formed in the
ribs by making them in two parts, which were glued together and clamped up
on the form while the glue dried, practically any number could be made which
would have the same curvature when thinned down to the proper thickness of
wall.

It was recognized at all times that the gluing together of the ribs not only
entailed extra work, but introduced an element of uncertainty unless some
kind of a varnish for the ribs could be found which would prevent any possi-
bility of the glue becoming soft from moisture in the atmosphere or from the
wings actually coming down into the water when the aerodrome was tried in
flight. A search was therefore made for a varnish that was water-proof. A
large number of different varnishes were tried, and one was finally found which,
after repeated tests, seemed to be thoroughly good. Several test ribs were
given three coats of this varnish, and were then kept immersed in water for 24
hours without the glue showing any signs of softening. It was therefore de-
cided to follow the plan of gluing the ribs together and protecting them with
three coats of this varnish, which seemed to possess the remarkable properties
of being not only impervious to water, but also unaffected by the application
of concentrated ammonia or of gasoline, either of which produces immediate
softening when applied to ordinary varnishes.

Following the indication of these tests that the hollow, round section, 22
mm. outside diameter by 17 mm. inside diameter, would probably give the best
eross-rib for the weight that it seemed possible to allow, a set of cross-ribs of
this form was constructed and put in place in the large experimental wing, in
which the former solid ribs had been tested. The wing was inverted and fast-
ened into two posts at the angle it would have in flight, the guy-wires from the

pine

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 199

lower guy-posts of the aerodrome being represented by wires stretched from
the posts. Im actual use on the aerodrome it was proposed to have three main
guy-wires running from each of the main cross-ribs to the lower guy-post, but
in the test, which is now to be described, the wires which would have come near-
est the body of the machine were lett off to see what effect their removal would
have on the wing.

The weight and dimensions of the wing, as set up, were as follows: Length
of the main ribs, 24 feet; length of the cloth covering, 22 feet; width of the
eloth covering, 11 feet; total weight, 29 pounds. The two main ribs (front rib
and mid-rib) were solid, 3.5 em. in diameter at butt, 2.5 cm. in diameter at tip,
and tapering from the middle to the tip. There were twelve regular cross-ribs
set 50.8 em. (20 inches) apart, each rib being as above described, 11 feet long,
22mm. outside diameter by 17mm. inside diameter at the butt, and tapering
from where they were attached to the mid-rib to the tip, and each weighing
300 grammes. There were two extra cross-ribs, one at the inner end next to
the body of the machine and the other at the outer end. These were solid strips
of wood 3.8 em. wide by 1.2 em. thick, made extra wide and stiff in order to with-
stand the strain of stretching the cloth covering. There was also a thin, flat
strip at the rear edge, which connected together all the tips of the cross-ribs,
holding them a uniform distance apart, and also serving to fasten the cloth.
The main mid-rib was stiffened in a vertical direction by a system of small guy-
wires drawn over short guy-posts about 6 inches high. With the wing inverted
and fastened in the way above described, a weight of 2 kilogrammes placed at
the inner rear corner produced a deflection of 26.7em. When the inner rear
corner was pulled up by a spring balance until the balance registered 2 kilo-
grammes, there was an upward deflection of 41.3em. When the main mid-rib
was held at the inner end, the pull of 2 kilogrammes, applied to the inner cor-
ner as before, caused an upward deflection of 25.4 cm. instead of 41.3 em. This
wing was afterwards given a sanding test under a weight of 0.7 pound per
square foot. With fine guy-wires fastened from the front of the ecross-ribs to
the tip and drawn just taut, the ribs showed an average deflection of 9 inches at
the tip under the above weight. When a small wooden guy-post was added
under each of these small guy-wires, the same weight produced an average de-
flection of 5 inches at the tip of each rib under the same load. In a previous
test of the wing, using hollow cross-ribs 16 mm. outside diameter by 10mm. in-
side diameter at the butt, and only half as far apart as the later ones, a load
of 1 pound per square foot on the wing produced an average deflection of 9
inches at the tip of each rib when the cross guy-wires on each rib were held
up by short guy-posts, but when these short guy-posts were removed, the same
load produced a deflection of nearly 25 inches at the tip of each rib.

200 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

Although this wing was a great improvement in every way over any of the
previous constructions, it was felt that it was too weak for the large aerodrome.
Further experiments were therefore made in order to secure a form of cross-
rib which would meet the rigorous requirements imposed. An inordinate amount
of time was spent in the construction and tests of various forms of rib, but as
a result a satisfactory cross-rib was at last constructed of the form shown in
Plate 66, Figs. 4-8, the dimensions at the three principal points, viz., first, where
the cross-ribs join the front rib; second, where they cross the mid-rib; and third,
at the rear tip, being given both for the intermediate cross-ribs and the end
cross-ribs.

Following the plan employed by Nature in the construction of the bamboo
pole, small partitions, approximately one millimetre thick, were placed every
three inches in the thin, hollow rib to keep it from being crushed. The parti-
tions were glued in place when the hollow rib was glued together on the form
around which it was bent and clamped until the glue dried. Longer blocks were
also inserted in each of the intermediate ribs at the point where it crossed the
main rib and also at the front end where it was attached to the front rib. In
the end ribs blocks were also inserted at the points where the cross-braces were
fastened to them for resisting the end stress due to the cloth covering.

Upon making up one of these ribs and testing it, it was found to possess
remarkable stiffness, so much so that it was thought probable that it was as
stiff in proportion to its size as the best thing that Nature had produced in the
bird’s wing. A large quill from the wing of a harpy eagle was therefore
stripped and the large end clamped in a special holder, and measurements were
made of the deflection produced by weights at various distances from the clamp.
As the main mid-rib of the wing of the aerodrome is placed approximately at
the point-of the center of pressure, the bending action on the cross-ribs may be
assumed to act on a lever arm from the mid-rib towards the front, and from
the mid-rib towards the rear in the cases of the pressure on the front and rear
portions of the wing, respectively. In testing these cross-ribs, therefore, against
the quill, the rib was clamped at the point where it crosses the mid-rib of the
wing, and measurements were made of the deflection produced by weights placed
at various distances from the point of clamping both front and rear.

The quill on which the measurements were made was 19.5 inches long and
had a gradual curve, the highest point of the curve being about the center of
the length of the quill, and the depth of curvature being about 2 inches. When
the butt of this quill was placed in the clamp the tip stood 17 cm. above the
horizontal. The hollow spruce rib, when clamped at a point 5 feet from the
tip (the point from which it tapers in both directions) had its tip 2.2 em. above
the horizontal, there being very little curve in that portion of the rib. The
quill weighed 4 grammes when stripped and 18 inches of it projected from the

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

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VOL. 27, NO. 3, PL. 67

SECTION AT TIP

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Cc

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 201

clamp which held it during the tests. The rear portion of the spruce rib pro-
jected 5 feet from the clamp, being thus 3.3 times as long as the quill, and it
weighed 120 grammes, the weight for the larger size having, therefore, increased
slightly less than the cube of the length.

The results of the tests of both the quill and the rib are given in the fol-
lowing table. The approximate cross-section of the quill at the point of clamp-
ing, the middle and the tip are shown in diagrams 4, 6 and C, respectively, of
Plate 67. The cross-sections of the rib at the corresponding points are shown
in diagrams D, FE and ’. The cross-sections of the quill, enlarged five times, are
shown in diagrams A’, Bb’ and C’.

QUILL FROM THE ReEMIGES OF HARPY EAGLE. Hoiitow Srruce Rts.
Weight, 4 grammes; length, 45 em.; tip, 17 cm. Weight, 120 grammes; length, 153 cm.; section,
above butt when the latter is horizontal. rectangular; tip, 17 em. above butt.
Point of Weight Point of Weight
application Absolute in terms Deflection application Absolute in terms Deflection
of weight in weightin of in terms ot weightin weightin of in terms
terms of grammes, greatest of length. terms of grammes. greatest of length.
length. weight. length. length,
0.39 1050 1.0 .38 0.39 15,000 1.0 Abt
0.445 605 0.58 38 0.445 11,400 0.76 Si int
0.56 A405 0.39 38 0.56 7,900 0.53 Al
0.75 210 0.20 08 0.75 4,000 0.27 Sit
0.95 77 0.075 38 0.95 2,000 0.135 sala

In each case the unit of length was the portion extending beyond the clamp;
the unit of weight, the greatest weight employed to produce the deflection. It
should be noted, however, that the relative deflection was quite different in the
two comparisons. In the case of the quill the deflection was 17 em. in 45 em., or
38 per cent; in the case of the rib it was 17 em. in 153 em., or 11 per cent. In
the case of the rib at the point 0.39 the absolute weight was 15,000 grammes,
the relative weight unity and the deflection in terms of length 0.11. While no
rigorous comparison can be instituted, since the rib was not deflected nearly as
much proportionately as the quill, yet the general inference is that while the
rib was not intended to be, and was not as elastic proportionately as the quill,
it was probably at least as strong in proportion to its weight. Briefly sum-
marizing these results it will be noted that the spruce rib was about 3.3 times
the length and 30 times as heavy, while it was 15 times as stiff near the butt and
26 times as stiff at the tip, as the quill.

As this test on the rib for the large wings had apparently shown that the
plan of constructing the ribs in the form of a hollow square secured maximum
strength for minimum weight, if was decided to construct a few sample ribs
after the same plan for the wings of the new quarter-size model of the large
aerodrome, and to test these ribs in a similar manner. The following table

shows the results of the test on one of these ribs:

Total length of rib = 80 cm. Curve = 1 in 18. Highest point of curvature = 0.25 from front.
Section of rib — 10 mm. X 14 mm. at point of attachment to mid-rib, tapering to 8 mm. X 12 mm.
at the front point and to 7 mm. X 2 mm. at the tip, The rib was clamped with the tip projecting

202 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

46 cm. and was weighted at different percentages of its length to such an extent that it was de-
flected 11 per cent of its length, or 5 em. The weight of the 46 cm. length of rib which projected
from the clamp was 11 grammes, the whole rib weighing 22 grammes and balancing on a knife edge

placed at the point where it was clamped.

Pointior psolu Weight i D i
application weight. erases ates
in terms of in greatest of

length. grammes. weight. length.

0.39 7680 1.0 0.11
0.445 5980 0.78 0.11
0.56 3680 0.48 0.11
0.75 2300 0.30 0.11
0.95 1100 0.143 0.11
1.00 930 0.121 0.11

A lighter rib than the above, which was constructed at the same time, was
also tested with the results shown in the following table. This rib was also
80. em. long, but was only one-half the linear dimensions in section of the rib
previously tested. The rear portion of it projected 46 cm. from the clamp. The
total weight of the rib was 11 grammes, or 5.5 grammes for the 46 em. on which
the measurements were made.

Point of aC . es
application Absolute Weighbin Detection
_of weight weight in greatest of
mae ee grammes. weight. length.

0.39 1400 1.0 0.411
0.445 1100 0.785 OAL
0.56 700 0.50 0.11
0.75 400 0.275 0.11
0.95 250 0.178 0.11
1.00 220 0.157 0.11

A still lighter rib of the same length, weighing 9 grammes, suitable for use
in the wings of the quarter-size model, was constructed and a set of tests was
made on it with the following results. As in the above test, 46cm. of the rear

portion of it projected from the clamp which held. it.

Point of : = 5

, Weight in Deflection

application Absolute = :

"of avenenit weight in fea OF wu te En)

pa ciia a grammes. weight. length.
0.39 1450 1.0 0.11
0.445 1150 0.795 0.11
0.56 740 0.51 0.11
0.75 380 0.262 0.11
0.95 210 0.145 0.11
1.00 180 0.124 0.11

Among quite a number of different forms of cross-ribs which were con-
structed of a size suitable for use in the model aerodrome, but made primarily
for use in tests to determine the best form to employ, may be mentioned the
following, in which both ribs were seven-sixteenths of an inch outside diam-
eter and five-sixteenths of an inch inside diameter. One was filled with elder
pith, formed up into a round rod that just fit the interior of the hollow rib, and
was @lued into it when the rib was glued up. The other rib was left hollow.
Upon testing these by suspending weights at different points, the rib without

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 203

the pith showed a slightly less deflection than the one with it, it happening
probably that the wood in one case was a little stiffer than in the other, al-
though they were carefully selected to be as nearly alike as possible. The rib
with the pith in it weighed 34 grammes and the one without it weighed 50
grammes. It was inferred from this test that the placing of a light pithy ma-
terial in the interior of the ribs would have no good effect, and would not only
add weight, but also complicate the construction. The reason for making this
test with pith in one of the ribs was that it was thought probable that the rib
flattened out somewhat when it was deflected under a load, and that the pith
stiffened with the glue with which it was fastened in, might lessen this.

As the ecross-rib described above, which was tested on October 23, 1899,
seemed in every way suited for use in the wings of the large aerodrome, a com-
plete wing equipped with similar ribs but of slightly changed dimensions, as
shown in Plate 66, Fig. 5, was immediately constructed. As previous tests had
shown that the wing covering did not ‘‘flute ’’ or ‘‘ pocket ’’ to any considerable
extent even when the ribs were as much as thirty inches apart, only ten cross-
ribs were used in this wing. The eight intermediate cross-ribs were of the
form described above, but the ribs at either end of the wing were made of a
larger cross-section and otherwise stiffened in order to resist the strain of the,
tightly stretched cloth covering.

On April 13, 1900, a final sanding test was made on this wing, guyed in a
manner similar to that used in the aerodrome, in which the following results
were obtained:

SANDING TEST OF LARGE WING.

Area, 260 sq. ft.; weight of wing, 29 pounds; weight of sand on wing, 231 pounds; total
weight supported by wing, 260 pounds, or one pound per square foot.
Deflection of cross-ribs, numbering from inner edge to extreme outer edge of wing—

Number of rib. Deteruon:
I Geleavys end Tid) eee ccweeciencinceeesenses Bb
Gh a5 ts oO HP OOU DOR DOU OD OSH rOOUGCIGOO0 C00KC 9.5
Dae eet Pe Sensor anny eh aleVelstalays.eccheie ofes ieleieisiwinleystnts 11.75
Ly ae oo Re oes ARAB OD OORIOE CUT DOU OOS OUIS UO LCtTG 12.25
Pe SSA RS hc COAG SOOO COD DOOD DC MCDMOOUC CG EC DTOD 12.5
(eee ated SiR G's Encino CD OCOD DO OOD Cobo UmOOTomtc 12.75
Lek e Ry SESE aE Boe buD atone CODD UDOnO Spurred 12.9
Cit A eee RO TRICO COORG O DODO nC 3.0
Cyn hoo AR aS fae ey GOGO OO DIEU O CHRD OUAG Ou FO GDL 12.0
10 (Heavy end rib) .......-.---eseeeeeeeeeees 9.75

The weight of sand put on the wing in this test was 1.5 times as great as
the pressure which at this time it was expected would be imposed upon it in
flight, and was in fact 1.2 times as great as the normal pressure when support-
ine the aerodrome as finally constructed. Even under this weight the greatest
deflection noted in terms of the total length of the rib was less than 0.10, show-
ing that the elastic limit of the rib was far from being reached.

204 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOlNOIT

As this test seemed to indicate that the wings constructed in this manner
were certainly strong and rigid enough for use on the aerodrome, and that im-
mediate further improvement could hardly be made, three similar wings were
at once constructed to complete the set. Somewhat later two additional wings
were provided, so that when the large aerodrome was taken to Widewater on
the Potomae in 1903 one and a half complete sets of wings were on hand, which
seemed to be ample to provide for any emergencies that might arise. ,

Each of these wings had, as is clearly shown in the drawings, Plates 53 and
54, two main ribs, which formed the main strength of the framework and gave
the wing longitudinal rigidity. To the main front rib were attached the cross-
ribs and the pieces for the curved extension later described. The mid-rib ex-
tended across the cross-ribs, parallel to and about 5 feet behind the front rib,
this being approximately the line in which lay the center of pressure of the
wing. It was upon this rib, therefore, that the greatest strain would fall.

The mid-rib, Plate 66, Fig. 2, was 731.5 em. (24 ft.) long, having at the butt
an outer diameter of 38mm. (1.5 in.) and an inner diameter of 25mm. (1 in.),
the walls being, therefore, approximately 6.5mm. (0.25in.) thick. From the
butt to the middle point the section was uniform, but from this point it had a
taper of one-twenty-fourth of an inch to the foot, so that at the tip it had an
outer diameter of 25mm. (1 in.), the thickness of the wall being unchanged. At
the butt end a wooden block 8 inches long was glued inside the rib, and at uni-
form distances of 75mm. (30 in.) 10 smaller blocks were glued in where the
cross-ribs were attached. The main front rib was of the same form and size,
except that it was some 2 inches shorter and had no blocks, except the long one
at the butt, glued in it.

To these main ribs were attached, in the manner later described, the 10
eross-ribs, to which the cloth cover was attached. The 8 intermediate cross-
ribs have already been described in connection with the tests. The cross-ribs at
the end of the wings, upon which greater lateral strains would come from the
stretching of the cloth, were made of the larger cross-section shown in Fig. 8
of Plate 66. Additional longitudinal stiffness was provided by gluing a strip
2mm. thick between the upper and lower halves, as shown in the section. These
end ribs, as well as those next to the ends, had small blocks glued into them
where they were crossed by the diagonal braces, in addition to the small parti-
tions 1 mm. thick, which were glued into the ribs every 3 inches to prevent crush-
ing, and the blocks 2.5 and 3 inches long respectively, where they were attached
to the front rib and to the mid-rib. At the extreme rear edge of the wing the
eross-ribs were attached to the small ‘‘D ’’-rib, which served to hold the ribs
at equal distances and to keep the cloth cover stretched tight. This ‘‘ D ’’-rib,
as shown in Plate 66, Fig. 3, had semi-circular walls 4mm. thick, 21 mm. in di-
ameter, to the edge of which was glued a flat strip 3 mm. thick.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 205

As originally designed the wings had a curve of only 1 in 18, the main
front rib forming the leading edge of the wing. Later, however, it seemed de-
sirable to ‘* quicken ’’ the curve and at the same time give the wing a sharper
leading edge. This was accomplished by attaching to the front rib, at the points
where the cross-ribs joined it, properly curved wooden pieces of the form shown
in Plate 66, Fig. 10, over which the cloth cover of the wing was stretched. The
curve of the wing after the addition of this extension is shown in Plate 66,
Fig. 4, and was a curve having a rise of approximately 1 in 12, with the high-
est point .25 from the front end.

On account of the large size of these wings and the consequent difficulty in
handling them it was necessary to construct them in such a manner that they
could be easily taken apart, rolled up, transported to the house-boat or any
other point where they might need to be used, and then quickly reassembled.
After much experiment as to the best means of constructing them, the following
plan was devised. The cloth covering was permanently fastened to the front
rib, to which were attached the front extension pieces by means of small metal
clips secured by small wood screws. On the rear edge of the front main rib,
at a uniform distance of 30 inches apart, 10 small metal horns of 1-mm. tubing,
5em. long, each brazed to an independent clamping thimble, as shown in Fig.
9 of Plate 66, were fastened. The front end of each of the cross-ribs was
slightly rounded out to fit the front main rib, and in the wooden block which
was glued in this end of the cross-rib a hole was bored to fit these horns. Each
of the cross-ribs was then pushed over its proper horn and against the front
main rib, and the cloth covering then drawn back toward the rear tips of the
cross-ribs. In the extreme rear edge of the cloth covering a seam was made,
and in this was inserted the ‘‘ D’’-rib already described. The cloth was then
tightly stretched and a wood screw forced through the ‘‘ D ’’-rib and into and
through the metal ferrule at the tip of the cross-rib. Near the inner and outer
edges of the cloth covering eyelets were placed about 6 inches apart, through
which small cords were ihen inserted and tied to the end cross-ribs. The main
or mid-rib was then placed on top of the cross-ribs and fastened to them with
wood screws, and the cross-braces were then fastened on the top of the wing, as
shown in Plate 54. The frame of the wing was stiffened horizontally by cross
guy-wires which passed from each cross-rib, at the point where the mid-rib
crossed it, to the adjoining cross-rib, at the point where it was connected to
the front rib. Each of the main ribs was individually guyed, in the manner
clearly shown in Plate 52, in order to stiffen it in the vertical direction, the fit-
tings for these guy-wires being shown in detail in Figs. 11-15 of Plate 66. Fi-
nally, small guy-wires were run from the front end of the cross-ribs over a
guy-post 12 inches high at the point where the cross-rib crossed the mid-rib
to the rear tip of the cross-rib. These cross guy-wires were regulated in tight-

206 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE von. 27

ness by raising and lowering a screw in the slot of the head of which they rested,
and which was threaded in the end of the small guy“post. Upper and lower guy-
wires, running from the main ribs to the guy-posts on the aerodrome, as al-
ready described, and as is clearly shown in the drawings, Plates 52 and 54, com-
pleted the guy-wire system for the wings, except for the drift wires,’’ which
for the front wings were run from the lower side of the mid-rib to the bow-
sprit at the front of the machine, and for the rear wings to the main frame.

Each wing when completely assembled weighed approximately 29 pounds,
and had a rectangular surface 22.5 by 11.5 feet (measured on the chord of the
curve), or 260 square feet, making the weight per square foot equal about 50
grammes, rather less than 1.5 times as much per square foot as the wings for
the steam-driven models. The total supporting surface of the aerodrome was
1040 square feet, and as the aerodrome when equipped for flight weighed, in-
eluding the aviator, 850 pounds this gave 1.22 square feet to the pound, or 0.82
pound to the square foot. Although this was a somewhat larger proportion
of weight to supporting surface than it had originally been expected to have,
there is every reason to believe that it was sufficient, for the quarter-size model,
when weighted so that it had 1.22 square feet to the pound, flew well, as will
later appear.

CHAPTER VII
EQUILIBRIUM AND CONTROL

Tn an aerodrome it is essential not only that its component parts shall be
so disposed that the initial equilibrium is correct and highly stable, but also
that some efficient means be provided for quickly and accurately restoring the
equilibrium, if for any reason it is disturbed. If the aerodrome is of sufficient
size and power to carry a human being it is, of course, possible merely to sup-
ply an efficient means of controlling the lateral and horizontal equilibrium of
the machine and depend upon the intelligence and skill of the operator, as de-
veloped by practice and experience, to maintain the proper equilibrium of the
machine while in the air. This method, however, is open to the objection that no
matter how skilled the aviator may be there remains the probability of a seri-
ous if not fatal accident as the result of any momentary lapse or diversion of
attention until the ‘‘ sense of equilibrium ’’ has been developed. One of the
chief problems, therefore, which had impressed itself from the beginning of
the work, was to devise some means by which the equilibrium of the aerodrome
would be automatically maintained under the varying conditions of flight, so as
to leave the aviator free, as far as possible, to control the direction of flight
and to devote his attention to other important matters connected with the
proper functioning of the various parts of the aerodrome. In the develop-
ment of the models it had been absolutely necessary to develop some efficient
automatic control, as they were far too small to carry an aviator, and the con-
ditions of flight in the open air, even on the calmest day, were such that con-
stant readjustments of the equilibrium were necessary. The suecess attained
in the automatic control of the equilibrium of the models had been so great,
and so much time would have been required for an aviator to acquire skill
sufficient to control a machine without such automatic equilibrium, that it was
considered both expedient and safe to embody in the large aerodrome the plans
which had proved so successful in the models. It was necessary, however, to
provide in addition in the large machine means whereby the aviator could quickly
and accurately either modify the action of the automatic devices or, if desired,
entirely supersede the automatic control by purely manual control. Three dis-
tinct problems were, therefore, encountered in connection with the equilibrium
and control of the large aerodrome. In the first place, the machine as a whole
had to be so designed, and its component parts so disposed as to secure a highly
stable initial equilibrium ; second, automatic means had to be provided for main-

207

208 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27
taining this equilibrium under the varying conditions of flight and for restor-
ing it if for any reason it was disturbed, and, finally, provision had to be made
for the quick and accurate control of the flight by the aviator. These prob-
lems, while intimately related, had to be met one by one and solved separately.

The general type of machine adopted was that which had been developed in
the years of experiment with the steam-driven models. From the very first
consideration of the large aerodrome, it seemed advisable to follow this type,
which not only had shown itself to be distinguished by remarkable longitudinal
and lateral stability in the tests, but was actually the only type in the world
which had at that time shown any possibility of successful flight. There was,
of course, a question whether single surface or superposed wings would be used,
and in spite of the negative results obtained in the tests of the models with
the superposed wings, it was felt that a considerable field for development was
open in this direction. However, in spite of the advantages which theoretical
considerations showed might be obtained through the introduction of this and
various other modifications of the original type, the whole teaching of past ex-
perience in the construction of the model aerodromes had been that success was
more certain to be achieved by following the course in which genuine practical
results had been achieved. It was decided, therefore, that in the construction
of the large aerodrome the design should follow as closely as constructional con-
ditions would permit the lines of the successful model Aerodromes Nos. 5 and
6, which have already been fully described.

The longitudinal stability of an aerodrome is largely dependent upon the
relation of three chief factors; the center of pressure, the center of gravity and
the line of thrust. For an aerodrome of the ‘‘ Langley ’’ type, the relative po-
sitions of these which give the greatest degree of stability had been determined
as far as possible through the years of experiment with the models. How-
ever, while it is the usual experience in designing machinery, or even scien-
tific apparatus, that what appears theoretically to be the best plan has to be
considerably modified for constructional reasons, yet in the design of an aero-
drome this is particularly true, for not only must all the various parts function
properly, both separately and as a whole, but this result must be secured for
the very minimum of weight. Experience alone can enable one to appreciate
thoroughly how seriously this consideration of weight complicates the problem.

In making the original designs for the large aerodrome it had been recog-
nized that the relative positions of the line of thrust, center of pressure, and
center of gravity were much better in model No. 6 than in model No. 5. From
Data Sheet No. 1, for Aerodrome No. 5 when it made its flight on May 6, 1896,
it will be noted that the line of thrust being assumed to be at the point 1500,*

1See explanation of system of locating points in Part I, Chap. II, p. 15.

———

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 909

the center of gravity was at the point 1497, and that, assuming the rear wings
to have two-thirds of the lifting effect of the front ones, the center of pressure
was calculated to be at the pomt 1498, or one centimetre in front of the cen-
ter of gravity, measured in the horizontal plane. In the vertical plane the cen-
ter of pressure was calculated to be at the point 2536, and the center of gravity
was found by test to be at the point 2501, when the line of thrust was assumed
to be at the point 2500, the center of gravity being actually one centimetre above
the line of thrust.

From the data sheet of Aerodrome No. 6, for its flight of November 28,
1896, it will be noted that the line of thrust being at the point 1500 the center
of pressure was at the point 1487, and the center of gravity at the point 1484;
that is, the center of pressure was three centimetres in front of the center of
gravity, measured in the horizontal plane. In the vertical plane, taking the line
of thrust at the point 2500, the center of pressure was at the point 2525, and
the center of gravity at the point 2486, the center of gravity being 14 centi-
metres below the line of thrust and 39 centimetres below the center of pressure,
the distance from the center of pressure to the line of thrust being, therefore,
64 per cent of the distance between the center of pressure and the center of
gravity.

As has been explained in Part I, while it is not desirable that the center of
gravity be a great distance below the center of pressure, as such a relation
tends to produce a special kind of rolling and pitching in varying currents of
air, it is highly desirable that the center of gravity should lie some distance
below the line of thrust in order that the three forces may be balanced. In a
macnine like model No. 5, where the center of gravity was actually, though
very slightly above the line of thrust, there is a constant tendency to produce
rotation of the aerodrome, if for any reason its equilibrium is disturbed, which
is corrected in practice by the action of the Pénaud tail. In model No. 6, on
the other hand, the disposition of the three factors was such that they tended
to maintain, rather than to destroy, the initial equilibrium of the machine.

These desirable relative positions had been made possible in model No. 6
by the fact that the center of gravity and line of thrust could be located at
practically any desired point, since with the use of steam the power plant con-
sists of two separable parts, the boiler, with its fuel and water tanks, and the
engine. These parts can, therefore, be placed in any part of the aerodrome that
constructional or theoretical reasons demand. Furthermore, the engine consti-
tutes such a relatively small portion of the weight of the entire machine that,
if for any reason it is desirable to place the engine in the same plane as the
line of thrust, its weight is not sufficient to alter materially the position of the
center of gravity, since the boiler, water and fuel tanks can be placed as low
as desirable and connected with the engine by suitable pipes.

210 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

With a gasoline engine, however, the conditions are very greatly altered.
Here the engine constitutes practically the entire weight of the power plant,
only such accessories as the ignition coil, batteries, and carburetor being avail-
able for lowering the center of gravity, unless the fuel, cooling water tanks and
radiator be placed below the engine and the liquids forced up by means of a
pump. In making the first designs for the large aerodrome, therefore, it was
found that it would be practically impossible to make the relative positions of
the center of gravity and line of thrust the same as had existed in model No.
6, however desirable it might be. The center of gravity could be brought ap-
preciably lower than the line of thrust only by placing the gasoline engine in
a plane considerably below that of the propellers, and this necessitated the ad-
dition of at least two more sets of gears with heavy bearings and braces. Be-
sides this almost prohibitive factor of weight, it was also foreseen that great
difficulty would be experienced in keeping even the two sets of bevel gears al-
ready necessary aligned and in proper condition for efficiently transmitting the
power to the propellers unless the frame and other parts were made prohibitively
heavy. It was, therefore, found necessary to bring the center of gravity prac-
tically in the same plane with the line of thrust, which made its general features
as regards equilibrium more nearly resemble those of model No. 5 than of
No. 6.

The weight of the aviator, it is true, constituted an appreciable part of the
flying weight of the large machine, and it at first seemed possible to lower the
center of gravity by placing him at a considerable distance below the line of
thrust. But it was recognized from the beginning that the aviator would prob-
ably have to give a great deal of attention to any form of engine in order to
insure its working properly, and his position must, therefore, be selected with
a view to the proper supervision of the engine and without regard to its effect
on the center of gravity.

Although the repeated successful flights of model No. 5 under varying con-
ditions of wind and power inspired the belief that the minor adjustments, as
well as the general plan of the large aerodrome, were such as to give highly
stable equilibrium, nevertheless, more direct corroboration of this opinion was
desired, and it was largely for this reason that the quarter-size model was con-
structed. In it every detail of the larger machine which in any way affected its
equilibrium was exactly reproduced to scale, and the greatest care was taken
that the same relative positions of the center of pressure, the center of gravity
and the line of thrust which it was proposed to employ for the large aero-
drome should be used on the model in its flight of August 8, 1903, which is
later described. The entire success of this flight, so far as the balancing was
concerned, in spite of the fact that the engine worked erratically and that the
launching speed was much less than it should have been, removed every doubt

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 211

that the equilibrium of the large aerodrome would be satisfactory under normal
conditions.

The second problem encountered in connection with the balancing and con-
trol of the large aerodrome was that of providing an efficient automatic means
for maintaining the equilibrium under varying atmospheric conditions. <Al-
though much had been done toward the solution of this problem in the devel-
opment of the models, the whole question was reopened and thoroughly recon-
sidered in designing the large aerodrome. The Pénaud tail, when made elas-
tic or when more or less rigid, but attached to the frame through an elastic
connection, and normally set at a negative angle, furnishes a means of auto-
matically controlling the equilibrium, which is sufficiently sensitive and accurate
to enable a machine to fly for a considerable distance, at least in moderately
calm weather, as is evidenced by the various flights of the model aerodromes,
where there was no human intelligence to control them. But owing to the prin-
ciple of action of the Pénaud tail, the flight of an aerodrome controlled by it
must of necessity be more or less undulatory in its course. Furthermore, the
tests with the models had indicated that, while the Pénaud tail served remark-
ably well as a means of controlling the equilibrium of the machine, provided the
balancing had been rather accurately determined, and, further, provided noth-
ing happened to affect seriously the equilibrium of the machine, it was limited
in its effectiveness by its narrow range of action. It was thought that a con-
trol mechanism which should be more sensitive and at the same time should act
more powerfully to prevent the upsetting of the equilibrium when the machine
was subjected to rather strong disturbing forces was desirable for any machine
which was to transport a human being and, therefore, involved the risk of a
fatal accident.

In the earlier period of the work and before the correct application of the
Pénaud tail to the model aerodromes had been found, Mr. Langley had planned
a large number of different forms of automatie control for preserving the equi-
librium of the machines. The more frequently recurring of these were devices
for changing the angle of the wings or tail, and others for shifting the wings
or tail bodily so as to shift the position of the center of pressure with respect
to the center of gravity, the motive power for operating the devices being in
some cases that derived from a gyroscope or a pendulum, and in others small
electric motor apparatus controlled by a pendulum or a gyroscope. Most of
these, however, never reached the stage of development where they were act-
ually tried on the machines in flight, as the tests of some of them in the shop
showed that they were unreliable, while others were abandoned either when
partly built or when only the drawines for them had been made. Among the
better-preserved models of devices for this purpose which were in existence
when the writer became associated with the work are those shown in Plate 68,

212 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOknaNt

where the piece at the top is a pendulum (inverted or direct) which controls
the movement of the horizontal tail by means of the cords and apparatus
shown, actuating these through the small electro magnets and apparatus at-
tached. Just below the rod, which represents a piece of the midrod, are three
parts, the first of which is a group of six little batteries clustered in a circle,
while next to it is a system of needles hung in gymbals, with electro-steering
apparatus in cups which itself turns on a graduated base, these electric con-
nections, together with the battery, controlling the vertical rudder. On the
right of this is another piece of apparatus for actuating windlass cylinders
which turn one way or the other as the contact is made by one side or the
other of the pendulum or the needle. At the bottom, on the two rods, is a tail-
piece which automatically throws the center of pressure forward or backward
according as the aerodrome departs one way or the other from the horizontal.

In spite of the fact that all the early attempts of Mr. Langley to devise
such a mechanical control had been very unsatisfactory, the idea that some-
thing of this kind was necessary had never really been abandoned by him. Here
was to be seen one of his chief characteristics, which was never to abandon any
idea that seemed valuable until it was brought to a successful issue or some
very strong proof was developed that the idea was impracticable. While on a
trip abroad during the summer of 1899, and especially while resting at Vallom-
brosa, Italy, Mr. Langley’s mind again turned to this problem, and he wrote
a number of very interesting letters emphasizing the importance of devising
such a mechanism which should be controlled by gravity. When he returned to
the Institution in the fall he insisted upon the same idea.

A mechanism which had been devised by the writer for another, but some-
what similar, purpose seemed to be well adapted to this end, and it was accord-
ingly decided to construct a small model of such a size as would be suitable for
use on one of the steam-driven models. The plan of control which it was pro-
posed to follow was to have some mechanism which would control the angle of
the tail through the action of gravity on a pendulum bob. Since it would re-
quire an exceedingly heavy pendulum should the deflections of it be directly
utilized to produce corresponding movements of the tail, the most feasible plan
seemed to be to have a light pendulum, which, while free to move under the
action of gravity, would nevertheless by its movement cause some outside force
to produce corresponding and simultaneous movements of the tail. The gen-
eral scheme of arrangement is shown in Plate 69, Figs. 1 and 2. This device
consists essentially of a cylinder (1) in which is mounted a piston with the
piston rod (3) passing through the cylinder head and connected to the cord (5)
which passes over the pulley (6), fastened to the tube (2), which is slidably
mounted on the midrod (7), whence it is carried over the pulley (8) on the guy-
post (9). From here it is connected to the spring (10) which is fastened by the

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MECHANISM OF CONTROL

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 213

bridle (11) to the upper side of the Pénand tail (12). The other end of the piston
rod (3) passes through the head in the other end of the cylinder, and has con-
nected to it a cord (14) which passes over the pulley (15) fastened to the tube
(2), whence it is continued over the pulley (16) and is joined to the spring (17),
which is connected by the bridle (18) to the lower side of the tail. Mounted
on top of the cylinder (1) is a valve chamber (20) having ports leading to the
two ends of the cylinder. Mounted in the valve chamber is a rocking valve sur-
rounded by a bushing having ports in it, and to which is fastened a rod (25)
which passes through the said valve and the head of the valve chamber. Fastened
to the rod (25) of the bushing is a lever (26), which by means of the link (27) is
connected to the piston rod (3). Fastened to the rocking valve is a rod (28) which
telescopes over the rod (25) and also passes through the same head of the valve
chamber, and carries at its outer end a pendulum (29) on the lower end of
which is the bob (30).

If steam or any other fluid under pressure is furnished to the valve cham-
ber through the pipe (31), none will be admitted to the cylinder so long as the
pendulum is vertical or at right angles to the axis.of the cylinder; and the tail
will be in its normal position, which we will suppose to be an upward inclina-
tion of five degrees. If, now, the front of the machine be depressed, thereby
causing the pendulum to move to the right, such movement of the pendulum
will cause the valve to open, admitting fluid to the left-hand end of the eylin-
der. This, acting on the piston, will force it towards the right, which, by means
of the cord, will cause the angle of the tail to be increased, thereby caus-
ing the rear of the machine to be depressed and the front to be raised. But as
soon as the piston begins to move under the action of the fluid pressure it simul-
taneously moves the bushing which surrounds the valve by means of the con-
necting links and levers, so that as soon as the piston has moved a distance
proportional to the amount that the valve has been opened by the pendulum,
it causes the bushing to shut off the port and thus prevents further fluid en-
tering the cylinder. As soon as the aerodrome responds to the action of the
tail the pendulum will, of course, begin to move back to its normal position
of perpendicularity to the cylinder, and will then open the valve to the other
port, thereby causing fluid to pass into the opposite end of the cylinder. This
fluid acting on the piston will move it in the opposite direction and thereby
cause the tail to be drawn back to its normal position at the same time that
the pendulum gradually reaches its normal position, owing to the return of
the aerodrome to its normal position. In the explanation given above it was
assumed that the slidable tube (2) was in a fixed position. It was planned to have
the equilibrium normally maintained automatically and at the same time permit
the operator to modify the automatic control and even to assume full manual
control. To secure this, the slidable tube (2) was connected at each end to an

214 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27
endless cord (20) which after passing over suitable pulleys was connected to the
control wheel (51) at the aviator’s car.

A model of this device was constructed in the spring of 1900 and was tested
with steam pressure in the shop. The test showed that the device acted imme-
diately and with precision, the piston performing movements simultaneously and
in exact accordance with the pendulum. The device, however, was never tried
in a flight of any of the aerodromes owing to the lack of time necessary to prop-
erly install it on the machine. Furthermore, it was thought probable that the
rapid acceleration of the aerodrome at the moment of launching would so dis-
turb the pendulum as to cause it to be in a very different position from that
of vertical, and also that the motion of the aerodrome through the air would
itself be a somewhat disturbing factor.

Because of the difficulties involved in this or any other mechanical device
for controlling the equilibrium, it was in every way advisable to retain in the
large machine the Pénaud system, which, though itself imperfect in many ways,
had been thoroughly tested in actual flight. In the models, it will be remem-
bered, the combined Pénaud tail and rudder controlled the longitudinal equilib-
rium by movement in the vertical plane under the combined influence of its ini-
tial negative angle and the elasticity of its connection with the frame, the flight
being kept as nearly as possible in a straight line by the vertical surfaces of
the tail. Although it was necessary that the large aerodrome should be
capable of being steered in a horizontal direction, it was felt to be unwise to
give the combined Pénaud tail and rudder motion in the horizontal plane in
order to attain this end, since the use of it for such a double function might
very seriously interfere with its proper action in preserving the longitudinal
stability. It was, therefore, at first thought best to dissociate the rudder and
tail so that the rudder might be used for horizontal steering without in any
way interfering with the proper functioning of the tail. But, as the main de-
sideratum was to obtain a flight of the large machine as soon as possible, and
perfection of steering control seemed secondary, it was decided, after further
consideration, in order not to risk the unpredictable effects that might result
from small changes, to duplicate on the large machine the combined Pénaud
tail and rudder of the model, and to add another rudder for steering in the
horizontal plane. Constructional requirements determined as the only avail-
able position for this rudder a rather disadvantageous one. As will be seen
from Plate 53, its efficiency was diminished by its being only about half as far
from the center of gravity as the combined -Pénaud tail and rudder, and by
beine located in the lee of a considerable portion of the frame, where it would
be subject to the cross-currents of air created by the forward motion of the

frame.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 215

For the preservation of the equilibrium of the aerodrome, though the avi-
ator might assist by such slight movements as he was able to make in the lim-
ited space of the aviator’s car, the main reliance was upon the Pénaud tail.
But, in the absence of any data for determining the effect produced in passing
from the model to the large machine, it could not be certain that calculations
based upon the balancing of the model would accurately determine the proper
balancing of the large machine. It was therefore decided to provide such at-
tachment for the Pénaud tail that, while it would always have elastic connec-
tion with the main frame, yet its angle could be appreciably changed without
affecting in any way the degree of elasticity of this connection. After many
changes in plans for securing this result, it was finally decided to arrange it
in the manner shown in the drawings. Referring to the general plans in Plates
53 and 54, and to the details in Fig. 1 of Plate 56, the main stem of the Pénaud
tail is seen to be connected by a pin to the horn (17), which is brazed to the clamp-
ing thimble, by which it is mounted on the vertical tube (16), suitably connected
and braced to the rear end of the midrod, the horn (17) being larger than the
stem of the tail and set at an angle to the vertical tube (16), the pin connec-
tion permitting the tail to swing up and down. The bridle (40), connected to
the center of the tail on its upper side, passes upward where it is connected
to the spring (41), the other end of which is connected to a single wire rope
(42), which passes over the pulley mounted ‘on the top of the post (43), which
is guyed to the upper guy-post by the wire (44). The wire rope (42), after
passing over the pulley, is connected to the spring (45), around the two ends
of which it forms a loop, and from there it passes down to the plane of the main
frame and through suitable pulley blocks to the aviator’s control wheel (50),
which is mounted on the starboard side of the main frame, convenient to the
aviator’s right hand when he is facing forward. From this point the wire
rope passes through the various pulley blocks towards the rear of the machine,
and through the pulley block (46) mounted on the side and near the bottom of
the rear lower guy-post. At a short distance beyond this pulley it is connected
to a weaker spring (47), the other end of which is connected by a second bridle
(48) to the under side of the Pénaud tail at its center. In order to prevent the
springs (41), (45) and (47), which furnish the elasticity for the Pénaud-tail
connection, from being strained beyond their elastic limit, either by a sudden
gust of wind or by the aviator attempting to move so large an area of surface
too suddenly, the wire rope (42) was made continuous around the springs, the
portion between the points where it was joined to the two ends of the springs
being made of such a length as to take the entire strain should the strain on
the cord become greater than sufficient to stretch the springs 50 per cent of

their original length.

216 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

In the construction of the equilibrium control wheel it was decided that
some arrangement must be secured whereby the wheel would normally be in-
active and maintain whatever position it had been set to, and at the same time
could be moved by the aviator with one hand, the mere act of grasping it ren-
dering it free to be moved, and whereby it must automatically lock itself in
any position in which it might be when the aviator removed his hand from it.
The multiplicity of things requiring the attention of the aviator made it desir-
able that his attention to any one of the important details, whether the engine,
the equilibrium, or the steering, should never require more than one hand, thus
leaving the other hand free either to hold on to the machine or to control some
other detail at the same time. While an irreversible wheel, such as would be
secured by the use of a worm and worm-wheel, at first seemed likely to answer
the purpose, yet the movement of a worm-wheel by means of a worm is neces-
sarily very slow if it is irreversible, and it here seemed desirable to so arrange
the wheel that in case of emergency, or for rising or descending, the aviator
could swing the Pénaud tail from its extreme upper position to its extreme
lower one by a small motion of his hand, and thus small or large adjustments
of the Pénaud tail could be intuitively felt to have been produced without the
aviator having to remember how many turns he had made of the wheel.

The control of the steering rudder was effected by a steering wheel (51)
similar in construction to the equilibrium control wheel (50), a continuous cord
(52) passing from the steering wheel through suitable pulleys to either side of
the steering rudder (7), springs being interposed in loops in the cord on either
side of the steering rudder to give some elasticity to the control apparatus in
order to prevent possible danger from the aviator attempting to move the rud-
der too suddenly. This steering rope passed directly through the steering rud-
der at the points where it was joined to it; so that, should one side of the cord
in any way become entangled with the frame or with its pulleys, the strain pro-
duced by the aviator in attempting to move it in the opposite direction would
be taken up by the cord and thereby avoid the possibility of destroying the
rudder. For even should the cord become entangled on one side, the rudder
could be given a slight amount of adjustment through the elasticity of the
coiled springs.

The design of the combined Pénaud tail and rudder followed very closely
that which had been used for the models, and its area of ninety-five square feet
on the horizontal surface with a corresponding area of vertical surface bore
the same relation to the area of the tail and rudder of the models that the area
of the wings of the large machine bore to that of the wings of its prototype.

While the provisions for automatie equilibrium and manual control were
not entirely ideal, even for the quiet atmospheric conditions under which it

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os

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 217

was proposed to make the first tests, nevertheless it was and still is believed
that the provisions for such conditions were sufficient to enable a successful
flight of a few miles to be obtained. It was thought to be very certain that,
once a successful flight could be made, the funds for the further prosecution
of the work would be readily forthcoming, and that when these funds were ob-
tained the many problems of control, rising and alighting, could be undertaken.

24

CHAPTER VIII
THE EXPERIMENTAL ENGINE

Tt will be recalled that the contract for the engine for the large aerodrome,
which had been entered into on December 12, 1898, called for its completion on
February 28, 1899. Between the time when the engine should have been com-
pleted and May, 1900, the engine builder had been engaged in a continuous
series of changes on it, all connected with what might be briefly called its proper
functioning. The actual mechanical construction of the more important parts
had been admirably executed, and this main portion of the constructional work
had been completed within the time called for by the contract. The trouble was
that the engine, which was of the rotary cylinder type, would not furnish any-
thing like the power which had been expected of it, and which the size and
number of its cylinders indicated that it should furnish. No one who has not
had practical experience in the development of gasoline engines, can understand
or appreciate how fourteen months could be spent in changes in the minor de-
tails of the engine with the expectation that each contemplated change would
bring success; and to anyone who has had experience in the matter, an attempt
to explain the delays would merely seem like a history of his own experiences.
It is, therefore, sufficient to say that the delay on the engine had now reached
a point where it was necessary to bring it to a successful completion imme-
diately or to abandon it definitely, and either find a competent builder who
had already built engines which, while not necessarily light, were successful,
and who would undertake to construct a light one on the same principles, or, as
a last resort, to turn to steam; and even the contemplation of this was appalling.

On May 6, 1900, the writer went to New York to see what could be done
towards assisting the engine builder to complete the large engine and also, if
possible, the small one which had been ordered for the quarter-size model later
described. He immediately made brake tests of the engine to determine ac-
curately just what effects were being produced by the different changes the en-
gine builder was making. Upon the first test the engine was found to develop
only 2.83 horse-power, and this could not be maintained for more than a few
minutes, when without any apparent cause and without any signs of overheat-
ing the engine would altogether cease to develop any power. After remain-
ing in New York for several weeks, during which time many changes were made
in the engine, he finally got it to the point where it would develop four horse-
power continuously; but, as it seemed impossible to get any better results with-

218

etl i

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 219

out an indefinite amount of experiment, it was decided that all lope of making
this engine an immediate success would have to be abandoned.

Interest in the development of the automobile was increasing at a rapid
rate all over the world, and while the builders in this country had not reached
the stage of development which had been attained in Europe, especially in
France, yet some American builders had succeeded in constructing cars pro-
pelled by gasoline engines which could be depended upon to run at least a short
distance, and it was, therefore, hoped that some one of the more competent of
these builders might be found who would undertake to construct a suitable en-
gine. After making a most extensive but fruitless search for such a builder in
this country, it was decided that it would be best to see what could be done in
Europe, and as other administrative matters made it necessary for Mr. Lang-
ley to go to Europe about the middle of June, the writer accompanied him to
see what could be done towards having a suitable engine built there. Some six
weeks were spent in visiting all the important builders of gasoline engines in
Europe, and the results were very discouraging. Everywhere the builders said
that they did not care to undertake the work, and that they did not consider
it possible to construct an engine of 12 horse-power weighing less than 100 to
150 kilograms (220 to 330 Ibs.), or that, if they had thought it possible, they
would already have built it, as they had had numerous inquiries for such en-
gines, and also wanted them for their own use. The last hope of securing a
suitable gasoline engine seemed to have vanished.

But, discouraging as was the refusal of the engine builders of Hurope to
undertake to build the engine, and still more so their opinion that such an en-
gine was an impossibility, inspection of the engines exhibited at the Paris Ex-
position had so strengthened the writer’s conviction of the possibility of the
undertaking that, before parting with Mr. Langley on August 3 to return to
America, he personally assumed the responsibility of building an engine which
would meet the requirements.

Upon returning from Europe on August 13, and finding that the engine
builder in New York had made no progress whatever towards improving the
engine during his absence, the writer condemned both the large engine and the
small one. The engine builder had practically bankrupted himself in his at-
tempts to construct these two engines, having spent something like $8000 or
$10,000 in actual wages over and above the contract prices for the engines, to
say nothing of remuneration for his own time or such expenses as shop rent
As all-of the money for the large machine and practically all for

and power.
assist him over

the small one had been advanced to him at various times to

financial stringencies—such advances, however, having been secured by suit-

able bonds—it was decided to take the various parts of the two engmes In

220 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

payment for the money which had been advanced, as it was hoped that some
of the parts of the engines might prove of use in experimental work.

Immediately after the writer’s return to Washington he began work on the
development of an engine. Taking some of the parts of the engine which had
been condemned and constructing others, he was able by September 18 to have
an experimental engine at work which, while not water-jacketed, but provision-
ally cooled by wrapping wet cloths around the cylinders, developed 183 horse-
power on the Prony brake at 715 R.P.M., the engine, including these wet
cloths, weighing 108 pounds. Of course these wet cloths sufficed to keep the
engine cool for only a short time—three to four minutes being the maximum.
This was only a temporary expedient for enabling the engine to run for a suf-
ficient time to make brake tests and determine the power it developed, but the
resuits obtained were so very encouraging that it was decided to make water
jackets for the cylinders of this engine and see what power it would then de-
velop for more extended periods.

This experimental engine, which was merely a ‘‘ patched-up ”’ affair, was
first equipped with a sparking arrangement built on the wiping-contact prin-
ciple. With this sparking arrangement several important difficulties presented
themselves, among which may be particularly mentioned the great difficulty of
so adjusting the sparking arrangements that the explosion in each cylinder oe-
curred at exactly the same point in its cycle that the explosions occurred in all
the other cylinders, it bemg necessary to secure this result to a reasonably
accurate degree in order to cause the engine to run smoothly enough to be
used in the aerodrome. Where an engine has a large and heavy fly-wheel run-
ning at a high rate of speed, the nicety of adjustment of the sparking arrange-
ment is not so essential, for the fly-wheel acts as a reservoir of energy and
tends to smooth out the rough and jerky impulses which would be otherwise
introduced by slight variations in the force of the explosions in the cylinders.
In constructing an engine for an aerodrome, however, the permissible weight
of the engine is so very small that the use of a fly-wheel having sufficient
weight to act as an energy reservoir is practically prohibited. Another seri-
ous difficulty which was encountered with the wiping-contact type of sparking
arrangement was that of keeping the stuffing boxes around the rotating con-
tact rods tight enough to prevent leakage, without at the same time binding
and causing excessive friction. Although it seemed probable that the difficul-
ties which have been mentioned, and other minor ones which were apparent,
could be remedied by further experiment, yet the high tension or ‘‘ jump-spark ”’
type of sparking apparatus seemed to offer much greater advantages. Since
it had fewer moving parts, and furthermore since the wiping-contact sparking ar-
rangement wouid have to be considerably modified in order to permit the con-
struction of water jackets around the cylinders, it was decided to construct a

|

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 221

new sparking arrangement for the engine on the jump-spark principle. After
introducing this change in the engine it was found to run very much more
smoothly and to require a minimum amount of care in adjusting it.

At the time that this engine was being developed it was practically im-
possible to obtain any outside information regarding the proper way of con-
structing it. The little that was then known had been learned through laborious
experience and at great cost by the experimenters who were attempting to
build automobiles, and was zealously guarded in the hope of preventing their
rivals from utilizing the results of their labors. It was the known custom,
however, of all engine builders at this time to use a separate spark coil and a
separate contact maker for each cylinder of an engine, no matter how many
cylinders there were. This multiplication of the spark coils, which at that time
were very heavy, not only added greatly to the weight but also had the same de-
fect that the wipe-spark type of sparking arrangement had of being exceed-
ingly difficult to so adjust that all of the contact makers would perform their
functions at exactly the same point in the cycle for each cylinder. To obviate
these difficulties, both of adjustment and of excessive weight, the writer devised
what is supposed to have been at that time a new and valuable multiple-spark-
ing arrangement whereby only one battery, one coil and one contact maker were
utilized for causing the spark in all five cylinders, a small commutat ing ar-
rangement in the high-tension circuit distributing the sparks to the proper cyl-
inders at the proper time. This form of sparking arrangement was found upon
test to work so satisfactorily that it was afterwards adopted for the small en-
gine of the quarter-size model, and also for the new and larger engine which
was afterwards built and which will be described further on. It is needless
to describe in detail the many and perplexing difficulties which were experienced
in procuring suitable spark coils, spark plugs and other appurtenances of the
sparking apparatus, all of which at this time were in a very erude state of
development, there being only a few different makes on the market, and most
of these being very unsatisfactory. One important minor improvement con-
nected with the spark plugs may be described, as the beneficial effect produced
by it was so very great that its use was continued in all future spark plugs for
all of the engines. This improvement, however, is now incorporated in many
of the plugs which are on the market, and in some eases patents, covering the
particular form in which the improvement is incorporated, are exploited by the
manufacturer. Considerable difficulty was at first experienced with the spark
plugs from a coating of soot (resulting from the incomplete combustion ofthe
gas and oil in the cylinder at the time of explosion) which formed on the por-
celain and thereby caused a short-cireuit, preventing the plug from working
properly. This was overcome by extending the metal portion of the plug for
some distance into the cylinder, and for something like three-quarters of an

222 SMITHSONIAN CONTRIBUTIONS 10 KNOWLEDGE VOL. 27

inch beyond the end of the porcelain insulator. The terminal which passed
through the insulator was also extended for something like half an inch beyond
the porcelain and bent to a proper extent to co-act with a piece of platinum
wire inserted in the interior wall of the plug which formed the other terminal.
After making this improvement in the plugs practically no difficulty was experi-
enced from short-cirenits caused by the soot.

In making the tests of this experimental engine it was found practically
impossible to absorb the power by a Prony brake in a sufficiently uniform man-
ner on account of the fact that the engine was being run without a fly wheel.
The consequent variation in the torque and speed during each revolution caused
such great fluctuations in the reading of the scales which measured the pull of
the Prony brake that no confidence could be felt in the accuracy of the readings
and, therefore, no confidence could be placed in the determinations of the effect
which different changes in the engine produced. A water-absorption dynamom-
eter consisting of a number of flat, circular discs fastened to a shaft and ro-
tating between other parallel flat discs arranged in a circular drum which was
filled to any desired extent with water was immediately planned, and the con-
struction of two of them was begun so that power could be taken from both
ends of the engine shaft, which, on account of its necessary lightness, was
apt to be injured by being twisted when all the power was taken from one
end of the shaft. In order to continue the tests on the engine while this
dynamometer was being made it was decided to employ one of the propellers
as a dynamometer. Although no accurate tests had been made to determine
just how much power was required to drive these propellers at various speeds,
yet the fundamental law was known that under the same conditions the power
required to drive any propeller would vary as the cube of the number of revo-
lutions, and since the Prony-brake tests had given an approximation as to the
amount of power which the engine developed at certain speeds, the law of the
propeller, and extrapolations from the data obtained in the tests of the smaller
propellers in 1898, enabled further approximations to be made as to the amount
of extra power which the engine developed when certain changes enabled it to
drive the propeller at increased speeds. This method had also the great ad-
vantage that, since the power required varies as the cube of the number of
revolutions, it is practically impossible for the engine to ‘‘ run away ”’ with the
propeller and cause serious damage through the possible excessive strains in-
troduced by high speed. This feature is also possessed by water-absorption
dynamometers of the type which were built and used in the later tests.

The construction of water jackets for this engine proved an exceedingly
formidable task, it being impossible to braze the jackets directly to the walls
of the cylinders without risk of ruining them. It therefore became necessary
to attach them by means of stuffing boxes, which, on account of their large size

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 223

aa0

and the necessity for keeping the weight a minimum, was a most difficult piece
of work. The work was rendered still more difficult by the fact that the water
jackets had to be made in halves which were brazed together after they had
been fitted over the head of the cylinder. Eyen when the work was done in
the most careful way this method of construction gave a great deal of trouble
from the leaking of the stuffing boxes or the jackets themselves. However,
after much delay, the water jackets were finally completed, and upon test the
engine was found to develop 21.5 horse-power at 825 R. P. M., the engine itself
weighing 120 pounds.

Further changes were made in this engine, especially in the pistons, a new
set of which were constructed which weighed 15 pounds less than the original
set. On account of the difficulty with the leakage of the water around the
stuffing boxes of the water jackets, and also from imperfections in the brazed
joints of the jackets themselves, it was found impossible to rely on the power
that the engine would develop at any particular time, as the water leaking
from the jackets and running down on the spark plugs of the lower cylinders
caused these cylinders to work erratically, and this not only materially reduced
the power but also caused jerky impulses in the absence of fly wheels.

It seemed so desirable to obtain as soon as possible a first test in actual
flight of the large machine that the writer offered to put this engine in the
aerodrome frame and make a test with it if the machine were launched over
the water, but with the launching track mounted directly on the river bank.
However, Mr. Langley felt it so necessary to make the initial test from the
top of the house-boat and at an elevation of 30 feet or more that he would not
consent to this, and as the engine at its best did not develop quite 24 horse-
power, which had been calculated as the minimum which should be provided,
it was thought unwise to attempt to make the first test from the top of the
house-boat until the aerodrome had been provided with engines that could be
depended on to develop continuously not less than 24 horse-power.

It then became necessary either to build a duplicate engine and use both
of them in the aerodrome, the original plan as already explained having been
to have two engines developing the 24 horse-power together; or, second, to con-
struct an entirely new engine large enough to furnish a minimum of 24 horse-
power and use this single engine.

As the construction and tests of this experimental engine had shown many
places in which the weight might be safely reduced, the writer decided to con-
struct an entirely new and larger single engine, and thereby avoid the extra
weight and difficulties which would be introduced by having to use synchroniz-
ing gears where two engines were used, it being impossible, of course, to run
the two propellers from the two engines independently without risk of serious
disaster.

294. SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL. 27

It will be recalled that when the aerodrome was originally planned in 1898
it was proposed to have two engines of 12 horse-power each, and the contract
for the single engine of 12 horse-power provided that a duplicate was to be
supplied, if desired, immediately upon the completion and delivery of the first
one. The calculations, both from the whirling-table tests and from the results
with the steam-driven models in actual flight, mdicated that 24 horse-power
would be ample for the aerodrome, which it was then expected would not ex-
ceed 640 pounds in weight, with a supporting surface of 960 square feet. But
it was found that the total weight of the machine was rapidly increasing on
account of slight mereases in the various details, which when added together
made a considerable increase in weight. Furthermore, as it had been found
difficult to keep all five of the cylinders of the experimental engine working
uniformly, it was thought best to build this new engine sufficiently large to pro-
vide not only the extra power necessary because of the increased weight of the
aerodrome, but also to provide for further inevitable increases in weight, and
over and above all this, to provide also that the engine would furnish all the
power necessary, even though one of its cylinders should absolutely fail to work
and act as a dead load on the others. The writer accordingly designed this new
engine to give 40 horse-power when all five of the cylinders were working, and
28 horse-power even though one cylinder should act as a dead load on the others.

The various materials for the construction of this engine were ordered early
in December, 1900, with the promise of delivery not later than January, 1901.
Owing to various causes, however, the major portion of the materials could
not be obtained until late in the spring, and, in fact, a portion of them were
not obtaied until the summer of 1901. During this period of delay, however,
the engine for the quarter-size model was completely reconstructed and further
tests were made with the experimental engine in developing accessories, such
as carburetors and spark coils.

The float-feed type of carburetor which was then coming into prominence
in automobile work proved at that stage of its development to be totally un-
suitable, as the slight but constant tremor of the aerodrome frame, when the
engine was working at high speeds under a heavy load, caused the float to act
as a pump and periodically flood the carburetor. This resulted in an irregular-
ity of action of the engine which at times injured not only the transmission
shafts, gears, and frame, but the engine itself by the serious pounding which
occurred. A form was next tried in which the gasoline was fed in through the
valve seat of a lightly loaded valve which raised whenever there was suction in
the inlet pipe, the amount of gasoline fed being regulated by a pin valve. Later
there were built several shapes and sizes of tanks filled with absorbent mate-
rial, which was saturated with gasoline and the surplus drawn off before start-
ing the engine. Some of these tanks were provided with a jacket through which

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT Dry

maw

a portion of the exhaust gases was passed in order to compensate for the cool-
ing of the tank caused by the evaporation of the gasoline. As a result of these
tests it was found that a type consisting essentially of a tank filled with small
lumps of a porous cellular wood (tupelo wood) which was initially saturated
with gasoline, and into which the gasoline was fed through a distributing pipe
as rapidly as it was taken up by the air, which was sucked throueh it by the
engine, gave the best results. Instead of jacketing this tank, the cooling effect
due to evaporation was compensated by drawing the somewhat heated air from
around the engine cylinders up through the loosely packed lumps of wood. When
tested in the shop this type was found to give such a very uniform mixture
that the engine ran as smoothly and regularly as an electric motor, the vibra-
tion in no way interfering with it, and even when the sudden change from a
state of rest to one of rapid motion through the air was imitated by suddenly
turning on the carburetor the blast of several large electric fans from various
angles, it was found to have no appreciable effect on the running of the en-
gine, thus indicating that the trouble which was experienced with the model
aerodrome in the trials of 1901 was not likely to be repeated with the large
aerodrome. Somewhat more than a dozen carburetors of various forms were
constructed before this last type was devised, but this proved so satisfactory
that there were never thereafter any carburetor troubles. In fact, as will later
appear, a carburetor of this type kept the engine on the large aerodrome run-
ning at full power not only when the aerodrome was in a vertical position in
the air, but also after it had turned completely over on its back.

CHAPTER IX
THE QUARTER-SIZE MODEL AERODROME

Owing to the very considerable changes which constructional reasons neces-
sitated in the relative positions of the center of pressure, center of gravity,
and line of thrust from those which theoretical considerations pointed to as be-
ing best, it was decided in January, 1900, to build a one-quarter-size model of
the large aerodrome, if a suitable engine capable of furnishing something like
one and a half horse-power could be procured without delay. It was hoped
that it might be possible to construct this model immediately without seriously
interfering with the progress of the work on the large machine, and that some
tests in free flight could then be made with it, which would give very much
more reliable data from which to determine the balancing of the large aero-
drome than had been obtained from the tests of the steam-driven models Nos.
5 and 6. A factor of uncertainty would still remain, due to the difference in
size between the large machine and the model, which could be determined only
by actual trial of the large machine itself; but by making the model an exact
duplicate, on a smaller seale of the large machine, very valuable results could
be obtained. Tests of it in free flight would involve, even with the probable
attendant breakages, a comparatively small expenditure of time and money.
A search was immediately begun for an engine builder who would undertake
to furnish a suitable engine for this model. The specifications called for an en-
gine developing one and a half horse-power on the Prony brake for five min-
utes without diminution in power caused by over heating. While it was desired
if possible to get an engine which would come within the given weight and de-
velop the required power for a longer time than five minutes, it was foreseen
that the construction of a multiple-ceylinder engine of so small a power made
it necessary to resort to the air-cooled type, and that such an engine would be
doing exceedingly well to develop its maximum power continuously for as much
as five minutes. The only engine builder who could be found willing to under-
take the construction of such an engine was the one already engaged in the
construction of the larger engine. As this builder was already twelve months
behind in the delivery of the large engine, it was felt that it would be unwise
to give it to him, both because the work on it might still further delay him in
the completion of the large one, and also because he was still having troubles
with the large one, which it was not certain he would ever be able to overcome.
After further consideration of the matter, however, it seemed so important to
have a model which was an exact duplicate of the large machine for the mak-

226

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT

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ing of tests, which might prevent not only serious damage but possibly fatal
accidents, that upon the assurance of the engine builder that the undertaking
of the small engine would in no way interfere with the completion of the large
one, a contract was entered into on February 23, 1900, which specified that the
engine should be delivered by April 1, with a penalty for any delay beyond
that date.

The frame for this quarter-size model was immediately begun and extra
workmen were employed for work on it in order that its construction should
in no way delay the completion of the large machine. The decision to construct
this quarter-size model of the large aerodrome had been made on the assump-
tion that, since it was to be one-sixteenth the weight of the large machine, and
therefore much heavier in comparison to its size than the steam models Nos.
5 and 6, it would, therefore, not need to be so carefully constructed in order to
obtain sufficient strength. But when construction was actually begun it was
found not only that the simpler and less expensive methods which it had been
proposed to use in joining its frame together resulted in a weak construction,
but also that the time consumed in tinkering up the imperfections in the joints
more than counterbalanced the extra time which would have been required to
make the joints in the best manner from the beginning. Before going very far
it was therefore decided to make the joints by following the same process which
had been developed in the construction of the previous models. The frame was
accordingly built in the most substantial manner, and when guyed by a system
of guy-wires similar to that employed for the large machine it was found to
be exceedingly stiff, in fact very much stronger and stiffer than the frame of
any of the preceding models.

In originally planning the model the intention was to make all its lear
dimensions exactly one-fourth those of the large aerodrome. Before the de-
signs were completed, however, it was seen from the previous experience with
the steam-driven models that instead of the 62.5-em. propellers, which a strict
adherence to the quarter-size plan would demand, it would be necessary to use
propellers which were at least one metre in diameter. Moreover, as the small
engine would be more than one-fourth the size of the engine under construe-
tion for the large aerodrome, a departure from the scale in the case of the
transverse frame would be necessary. The designs were therefore altered so
as to admit of using the larger propellers, and the tubes which formed the front
of the transverse frame were bent, as shown in the plan photograph, Plate 70,
in order to give a large enough space for properly mounting the engine.

The frame with these modifications was completed in June, 1900, but no
engine was ready for it, as the builder had failed to fulfill his contract for either
the large or the small engine, although several trips to New York had been

made to expedite their successful completion.

228 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE Viola

Soon after this it became certain that the engines for both aerodromes
would have to be constructed in the shops of the Institution, and owing to the
greater importance of the experimental engine for the large aerodrome, all the
facilities of the shops were devoted to the early completion of it. In Novem-
ber, 1900, however, it was seen that the experimental engine alone would not
furnish sufficient power for the large aerodrome, and that a duplicate of it
would have to be built or a new and larger engine designed and constructed,
and that therefore it would be impossible to get the first tests of the large aero-
drome in free flight before the following summer. It was therefore decided
that it would be best to suspend work temporarily on the large aerodrome and
its engine, and put all the workmen who could possibly be employed on the con-
struction of the small engine, so that it would be ready in time to permit some
tests of the quarter-size model to be made during the following spring.

In order to expedite its construction as much as possible, the attempt was
made to utilize all the available parts from the small engine which had been
undertaken by the engine builder in New York. The cylinders, which it had
been expected would be kept cool by their rotation around the crank pin, were
not well adapted for use as stationary cylinders, since they were not provided
with radiating ribs, but it was hoped that by using them an engine could be very
quickly constructed which would keep cool long enough to enable some short
flights to be made with the model.

The work on this small engine was pushed forward very rapidly, so that
within a short time it was sufficiently complete to allow some power tests to be
made with it. In the first of these tests the attempt was made to measure the
power by means of the Prony brake, but as the engine had no fly wheel the
fluctuations in speed during each revolution were so great as to make it im-
possible to obtain readings of any value. When it was attempted to remedy
this by putting a fly wheel on either side of the crank shaft of the engine, it was
found that the sudden starting of the engine caused such severe strains in the
erank shaft, which had been built strong enough for driving the propellers but
not for suddenly starting fly wheels having considerable inertia, as to make it
unsafe to continue the use of fly wheels. As without them the Prony brake could
not be used, it was decided to build a small water-absorption dynamometer on
the same principle as the larger ones which were under construction for the large
engine. As this larger dynamometer has already been described, it is only nec-
essary to add that the small one consisted of twelve rotating plates and twelve
stator plates twelve inches in diameter. In order to avoid the construction of
a special and elaborate testing frame for mounting the engine and the dyna-
mometer exactly in line with each other, it was attempted to connect them by
means of a universal joint. This ‘‘ short cut ’’ also proved the ‘‘ long way
around.’’? The strains set up in the universal joint by the sudden starting of

i

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 229

the engine caused so much trouble on account of the inertia of the rotating
plates of the dynamometer that the time lost in keeping the universal joint in
working order during the tests more than counterbalanced the extra time which
would have been required to construct a special wooden frame on which the
dynamometer and engine could have been mounted in line with each other so
that the crank shaft of the engine could have been directly connected to the
shaft of the dynamometer.

Much time was also lost in the effort to construct an apparatus by which
a record could be obtained of the power actually used in propelling the aero-
drome. Various methods were in use by which the thrust of the propellers
could be more or less satisfactorily measured while the aerodrome was at rest,
but it was desired to know just how much power the aerodrome consumed while
in actual free flight. Such a record it was hoped to obtain from a device in-
corporated in the propeller shafts. This thrust-measuring device consisted es-
sentially of a propeller shaft made in two sections, one section telescoping the
other for a short distance. On the section of the shaft to which the propeller
was attached there was mounted a drum, having in its circumference two long.
slots diametrically opposite. To the other section of the shaft a dise was fast-
ened with two diametricaily opposite rollers mounted on its periphery, which
fitted the slots in the drum of the other section. A compression spring was inter-
posed between the dise and the drum, and the outside of the drum was so arranged
that a strip of paper could be wound around and fastened to it which would serve
as a chronograph sheet. A pencil was fastened to the frame, and, since the drum
was connected to the section of the shaft to which the propeller was attached and
which therefore moved to and from the frame under the action of the propeller
thrust, a record of the actual thrust of the propeller at any particular moment
could be obtained by simply pressing the pencil up against the paper on the drum
and calculating the thrust from the calibration of the compression spring. Since
the thrust would naturally be greater when the propellers were revolving in
a moored condition, during the few moments after the engine was started up
and before the aerodrome was launched, it was necessary to provide means for
having the pencil point held away from the chronograph sheet until the aero-
drome was launched, and then have the point come to bear on the sheet. This
was accomplished by having the point held off by a small trigger arrangement
which was to be released just at the moment that the aerodrome left the launch-
ing car. <A set of propeller shafts embodying this thrust-recording device was
constructed, but when they were actually tested on the aerodrome many diffi-
culties were encountered which had not been anticipated. In the first place
the gasoline engine for the model was started up (or ‘‘eranked over ’’) by
turning the propellers by hand. A gasoline engine never starts slowly, and on
account of this suddenness of starting causes a very great strain in any shaft-

230 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

ing by which it is connected to any driven mechanism. The inertia of the driven
mechanism, even though it be apparently small, becomes a most serious matter
when an attempt is made to start up very suddenly. This effect is very much
intensified if the driven mechanism is connected to the engine through even one
pair of gears, for there is always a certain amount of back-lash between the
teeth of the gears, and the effect of this back-lash is still further intensified
when the driven mechanism is turned over by hand in order to start the éngine,
as this takes up the back-lash on one side of the gears, and the moment the en-
gine starts permits a free movement until it suddenly takes up the back-lash
and strikes the other side of the gear teeth with a blow. The effect of this
sudden starting of the engine proved most disastrous to the thrust-recording
devices, and, although they were considerably strengthened, it was found after
a short time that in order to make them strong enough to withstand the shock
of the sudden starting of the engine it would be necessary to make them in-
ordinately heavy. It was therefore decided to abandon all attempts to incor-
porate the thrust-recording device on this quarter-size model, but it was hoped
to install it later on one of the steam-driven models, where the engine starts so
slowly that there would be no need for excessive strength in it.

The engine for the quarter model when reconstructed with stationary in-
stead of rotating cylinders was found in the shop tests referred to above to
develop when working at its best between 1} and 2 horse-power, as measured
by the absorption dynamometers. However, it was impossible to maintain this
power steadily for more than 30 seconds. In the first place, the same difficulties
(heretofore described) that were met with in securing a suitable carburetor for
the experimental engine were experienced at the same time in the development
of the small engine. In the second place, as the engine had no cooling apparatus
of any kind, it was found that it could not be tested in the shop for more than
30 seconds owing to premature explosions. It was hoped, however, that by hav-
ing everything ready for a flight before starting the engine, it might be pos-
sible to launch the aerodrome before the cylinders began to heat seriously,
and that the greatly increased cooling effect due to the motion of the aerodrome
through the air would permit the engine to develop sufficient power to secure a
flight that would show whether or not the balancing was correct, as the final
disposition of some of the accessories on the large aerodrome could not be so
well settled until it was known just how the calculated balancing of this new
model corresponded with the actual balancing necessary for flight.

On aceount of Mr. Langley’s reliance on the generally sound theory that
where a successful method of conducting an experiment has been found only
after a lone series of failures it is best not to change to some unknown and
untried plan, it was impossible, especially where failure in the test might in-
volve a fatal accident, to get him to deviate from his original plan of launch-

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT Zo

ing the large aerodrome from the top of the house-boat. He apparently re-
alized as well as anyone, that in many respects the making of the test from
the top of the house-boat had many serious drawbacks, but he emphasized and
impressed on the writer the importance of following as far as possible in the
construction and test of the large machine, the plans which had brought sue-
cess with the models. Believing, however, that there was probably a better
method of launching the aerodrome than from the top of the house-boat, and
that it would be well to prepare before hand as far as possible for following
some other plan of launching immediately after a first successful test had been
obtained from the top of the boat, Mr. Langley had constructed some floats
which were arranged to be attached to the launching car of the quarter-size
model so that the car could be converted into a catamaran raft. It was not be-
lieved that this crude arrangement would suflice for a complete launching appa-
ratus, since the power of the aerodrome propellers would not be great enough
to force the raft through the water at a sufficiently high speed; still it was
thought that by having the launching car arranged in this way the model might
be allowed to drive the raft rapidly through the water and thus give some idea
as to what would be necessary, in a more complete launching apparatus, to ob-
viate the danger of the drag of the raft causing the model to plunge over head-
long into the water. The launching car with these floats attached to it, and
with the quarter-size model mounted on the car, is clearly shown in Plates 73
and 74.

While the results obtained with superposed wings in the tests of models
Nos. 5 and 6 in the summer of 1899 indicated that the ‘‘ single-tier ’’ surfaces
were much more efficient, still, as has been already stated, the great advantages
of the superposed surfaces, so far as strength of construction is concerned, was
fully realized at all times. As a result of these tests it was decided to use
the ‘‘ single-tier ’’ surfaces in the first test of the large machine in order to in-
sure as far as possible the best conditions. However, it was from the begin-
ning planned to construct superposed surfaces for use in the later tests of
the large machine; and, in order to obtain more reliable data on such surfaces
than had been obtained in the tests of the models in the summer of 1899, a
set of superposed surfaces for the quarter-size model were constructed during
the winter of 1900-1901. The quarter-size model, equipped with these surfaces,
is shown in Plates 75 and 76, where the model is seen mounted on its launch-
ing car, which is attached to the floats heretofore referred to. It was originally
planned not to employ guy-posts when using the superposed surfaces, but after
the latter had been constructed and attached to the frame, it was found that
they would have to be made with rigid joints instead of hinged joints if the
guy-posts were omitted. As the hinged joints, however, were already made,
and permitted the surfaces to be folded up so as to occupy a much smaller

>

232 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE voL.. 27

space in shipping them, it was decided to retain the hinged form of construc-
tion and use the guy-posts as shown in the above plates.
After much delay, due to various causes, the quarter-size model, as shown
in plan, end elevation, side elevation and three-quarter elevation in Plates 71
and 72, respectively, was taken down the river in June, 1901, in order to make
some tests with it from the small house-boat, which had been previously moved
to the middle of the river opposite Widewater, Va. A test of it in free flight
was made on June 18, its condition at this time being shown by Data Sheet No.
2 in Appendix. The launching apparatus worked perfectly and the aerodrome
‘started off on an absolutely even keel, dropping only a few inches immediately
upon leaving the launching apparatus, and continuing straight ahead directly
into the light wind of something less than 2 miles an hour. After it had gone
only about 100 feet, however, it began to descend slowly, but still maintained a
perfectly even balance, and finally touched the water about 150 feet from the
house-boat, having been in the air between 4 and 5 seconds. It was imme-
diately recovered, and as soon as the wings could be dried out another test was
made, as it was thought probable that the wind had interfered with the car-
buretor to such an extent that the engine had not received the proper mixture
of gas. Upon this second test the launching apparatus again worked perfectly
and the aerodrome again flew straight ahead on a perfectly even keel, and at a
uniform height from the water until it had gone about 300 feet, when it again
began to descend slowly and finally touched the water about 350 feet from the
house-boat, having been in the air about 10 seconds. While the tests were very
disappointing, owing to the extreme brevity of the flights, yet they showed con-
clusively that the balancing of the aerodrome was correct, at least as far as
motion in a straight line and in a quiet atmosphere was concerned. As one
and a half horse-power, which was felt to be the very minimum which would
successfully propel the aerodrome, was furnished by the engine only when work-
ing at its very best, and as the change in conditions from a quiet state to a
velocity of something like 40 feet per second evidently caused a considerable
drop in the power because of the change in the gaseous mixture which the ecar-
buretor furnished to the engine, it was decided not to make any further test of
the aerodrome until the engine cylinders could be reconstructed so as to pro-
vide more effective means for cooling it, and thereby a reasonable margin of
power above that actually necessary. The aerodrome was accordingly returned
to Washington for the purpose of making new cylinders for the engine. In
constructing these new cylinders the old cylinder heads from the previous eyl-
inders were used in order to expedite their completion. This proved in the
end to be a very great mistake, though at the time it seemed probable that the
use of them would save much delay and considerable expense. The new cyl-
inders were constructed of steel tubing originally one-half inch thick, which

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 233
was machined to the form clearly shown in the photograph, Plate 77, where it
will be seen that thin radiating ribs spaced one-quarter inch apart were formed
integral with the cylinder, the combustion chambers or heads being screwed on
and brazed to the cylinders. After much delay the new cylinders were com-
pleted, and upon test it was found that while the radiating ribs assisted very
greatly in keeping the engine cool, yet the valves were so small that the gas
was not able to get in and out of the cylinders rapidly enough to permit the
engine to furnish its full power. Even at this stage it would have been better
either to have made new eylinder heads with larger valves or to have made
entirely new cylinders and cylinder heads, but in the effort to economize time
and money it seemed best to try to overcome part of the defect by adding an
auxiliary inlet valve. This was constructed, and upon test it was found that,
although the engine developed 3.2 horse-power on the Prony brake at 1800
R. P. M., and even maintained 5.1 horse-power on the brake for a few seconds
when running at 3000 R. P. M., the ports leading from the valve chamber to the
eylinders were so small that they became heated after the engine had run for
2 minutes and premature ignition occurred, which, of course, immediately and
very greatly reduced the power developed.

It was decided, however, in view of the tests in which the engine had de-
veloped 3.2 horse-power at 1800 R. P.M., that there was sufficient margin of
power to enable it to propel the quarter-size model, even if it was not work-
ing at its best. After concluding the Prony-brake tests on the engine, it was
mounted in its proper position in the aerodrome frame and connected to the pro-
peller shafts. Some pendulum tests were then made, showing an average lift
of approximately 57 per cent of the total flymg weight. But it was found that
the propeller and transmission shafts and their bearings would not stand the
strain due to the increased power of the engine. Newer and stronger shafts
and bearings were, therefore, constructed and further pendulum tests were
made. It was then found that the transverse frame which supported the shafts
and bearings was too weak, and this was strengthened by substituting newer and
thicker tubing where it seemed necessary.

These changes and repairs were all completed by October, 1901, and the
quarter-size model was at last, after months of delay, felt to be in a condition
which justified the expectation that its next flight would be entirely successful.
In view of the much more important work on the large aerodrome which de-
manded immediate attention the quarter-size model in this completed condition
was put aside. Nothing more was done with it until April, 1903, when some
shop tests were made preliminary to taking it to Quantico, where, on August
8, it made a successful flight, which is described in Chapter XIL

26

CHAPTER X
CONSTRUCTION AND TESTS OF THE LARGE ENGINE

The main requirement in an engine for an aerodrome—aside from relia-
bility and smoothness of operation, which are necessary in an engine for any
kind of locomotion—is that it shall develop the greatest amount of power for
the least weight. It is, therefore, desirable to reduce the weight and number
of parts of the engine to the very minimum, so far as this ean be done with-
out sacrificing reliability and smoothness of running. Furthermore, since the
strongest metal for its weight is steel, and since the greatest strength of steel
is utilized when the stress acting on it is one of tension, it is advisable to de-
sign the engine so that the parts which sustain the greatest strains shall be
of steel and, as far as possible, meet with strains which are purely tensional
ones.

In designing the new engine for the large aerodrome it was, therefore,
planned to make it entirely of steel, as far as this was possible. The only
parts which were not of steel were the bronze bushings for the bearings, the
vast-iron pistons, and cast-iron liners of the cylinders. Previous experience had
shown that, while it is possible to use a-cast-iron piston in a steel cylinder or
even a steel piston in a steel cylinder, provided the lubrication be kept exactly
adjusted, yet the proper lubrication of the piston and cylinder of a gas engine
is difficult even under the most favorable conditions, owing to the fact that ex-
cessive lubrication causes trouble from the surplus oil interfering with the spark-
ing apparatus. It was, therefore, determined not to risk serious trouble by at-
tempting to have the pistons bear directly on the steel walls of the cylinders.

While visiting the French engine builders in the summer of 1900 in the at-
tempt to find one willing to undertake the construction of a suitable engine for
the aerodrome, it was pointed out to them that the great amount of weight
which they claimed to be necessary for the cylinders, and which they stated
made it impossible for them to build an engine which would meet the require-
ments as to power and weight, could be very greatly reduced by making the
cylinders in the form of thin steel shells having cast-iron linings. All, how-
ever, to whom this suggestion was made declared that it was impossible to build
satisfactory cylinders in this way; some of them even stated that they had tried
it and found it impossible to keep the thin liners tight in the steel shells. The
difficulty which they had encountered is due to the difference in expansion of
the steel and the iron when raised to a rather high temperature by the heat of
the explosions, if the cylinders are not well jacketed with water; and if the steel

99
293

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 235

shells are water jacketed they then do not expand as much as the cast-iron
liners, and this causes the latter to become ‘‘ out of round ’’ because of the
compression strains produced in them when trying to expand more than the
steel shells. As past experience had shown, however, that it was possible to
keep the liners tight in small cylinders, it was believed that by taking proper
care in the construction there would be no difficulty in this respect with the
cylinders of this larger engine.

In carrying out these plans, however, of making the cylinders of steel,
numerous constructional difficulties were encountered which could not be fore-
seen when the design was made. Had they been foreseen, provision for obvi-
ating them could easily have been made. As will be seen from the drawing,
Plate 78, the engine cylinders consisted primarily of a main outer shell of steel
one-sixteenth of an inch thick, near the bottom end of which was screwed and
brazed a suitable flange, by which it was bolted to the supporting drum or crank
chamber. These shells, which were seamless, with the heads formed integral,
were designed to be of sufficient strength to withstand the force of the explo-
sion in them, and, in order to provide a suitable wearing surface for the pis-
ton, a cast-iron liner one-sixteenth of an inch thick was carefully shrunk into
them. Entering the side of the cylinder near the top, was the combustion cham-
ber, machined out of a solid steel forging, which also formed the port which
entered the cylinder and was fastened to it by brazing. The water jackets,
which were formed of sheet steel .020 inch thick, were also fastened to the cyl-
inder by brazing, and it was in connection with the brazing of these water jack-
ets that the first serious difficulty was met in the construction of the engine.
In the first place, as the jackets were of an irregular shape and of a different
thickness of metal from the walls of the cylinder to which they were joined,
the expansion and contraction due to the extreme heat necessary for properly
brazing the joints caused such serious strains in various and unexpected direec-
tions that it was only by exercising the very greatest care and patience that
a completely tight joint at all points of the jacket could be secured. In the see-
ond place, the size of the cylinders and the consequently large extent of water-
jacket surface, complicated the problem. The maintenance over this large sur-
face of the extreme heat necessary for brazing involved discomfort and, indeed,
actual suffering to the person engaged in the work, and much care and skill
were demanded in so distributing the heat that the temperature of the surface
of the jackets would be uniform enough to prevent serious strains from expan-
sion and contraction. As no workman could be found either competent to do
the work or willing to undergo the personal discomfort, the writer was obliged
to do all this brazing work himself. Besides the difficulties due to the expan-
sion and contraction of the jackets while they were being brazed, the greatest
eare had to be exercised to avoid heating the cylinders so hot as to weaken the

236 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOT eT

joint where the explosion chambers were joined to the cylinders, which, of
course, had been brazed before the jackets were fitted to them preparatory to
brazing them.

Another great difficulty was that the ring which encircled the cylinder near
the middle of its length, and which formed the bottom part of the water jacket,
expanded very much more than the cylinder itself, so that, if it was brazed to
the cylinder before the jacket was brazed to it, the heat of brazing the jacket
to the ring would cause the ring to break loose from the cylinder; while if the
ring was not previously brazed to the cylinder, but was brazed after the jacket
had been brazed to it, the very much greater heat required for brazing the ring
to the cylinder caused the spelter to burn out of the joint between the jacket
and the ring. Furthermore, it was found very difficult to braze the two joints
at the same time, since in brazing the ring to the cylinder it was best to have
the eylinder in an inverted vertical position, so that the spelter could be made
to flow evenly around the ring and form a fillet against the wall of the cylin-
der, while in brazing the jackets to the ring it was best to have the cylinder
in the reverse vertical position or lying on its side so that the spelter could
properly flow into this joint. Finally, however, after what proved to be most
exasperating and tedious work, the five cylinders necessary for the engine were
completed and a series of tests was immediately made. During the course of
these tests the water circulation became obstructed in several instances, and the
consequent high temperature to which the cylinders and jackets were raised
caused severe strains in the jackets which, in turn, produced breaks in the
brazed joints. These breaks had to be rebrazed, and in brazing them it was
necessary in almost every case to remove the cast-iron liners and rebraze the
entire jackets from start to finish, as the application of the intense heat neces-
sary for brazing at any one point produced such severe strains that before the
break which was being repaired could be completed other breaks developed at
various points of the jacket. It was, therefore, necessary to get the whole jacket
up to a fairly uniform heat and complete the brazing while it was in this con-
dition, and then keep the whole cylinder at a uniform but gradually decreasing
temperature until it had sufficiently cooled off.

On account of these troubles with the water jackets and the cylinders, it
was decided to build some extra cylinders, not only because past experience
had suggested improvements in detail in the construction of the jackets, which
would prevent to a large extent the great troubles which had been met with
in the brazed joints, but also to insure having sufficient cylinders to enable the
engine to be always in working condition, even though several of the cylinders
might be out of commission from slight imperfections in the jackets or at other
points. While the construction of these new cylinders involved a repetition of
the arduous task of brazing, yet the minor improvements which were introduced

VOL. 27, NO. 3, PL. 78

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 237

proved eminently successful in providing against future troubles from leaky
jackets.

The general form of construction of the engine with the improved cylin-
ders will be readily understood from the drawings, Plates 78-81, in which Plate
78 is a detail sectional view, previously referred to, through one of the cylinders ;
Plate 79 is an end elevation of the port side, Plate 80 is a plan view, and Plate
81 is an elevation of the starboard bed plate which supports that side of the en-
gine, and by which it was fastened to the aerodrome frame, this view showing
particularly the sparking apparatus which was mounted on the bed plate. The
engine consists primarily of a single crank shaft provided with a single crank
pin, the shaft having bearings in a drum which consists essentially of two heads.
Arranged around the crank shaft and attached at equidistant points of the drum
are five cylinders. Mounted on the port side of the crank shaft and close to the
erank arm is a small gear, which through suitable gears mounted on the port
head of the drum drives a double-pointed cam which has a bearing on the ex-
terior of the hub of the drum. The ratio of these gears is such that the cam
is driven at one-quarter the speed of the crank shaft, and in the reverse di-
rection. Mounted on the exterior side of the port head of the drum are five
punch rods, the upper ends of which are within a sixty-fourth of an inch of be-
ing in contact with the exhaust-valve stems of the cylinders, and on the lower
end of these rods are hardened-steel rollers which rest on the double-pointed
cam—this one cam thus serving to operate the exhaust valves of all five of the
cylinders. The port head of the drum is connected to the port bed plate, by
which it is supported, by means of a flanged bushing in which are formed
tongues and grooves which fit into corresponding grooves and tongues formed
in the hub of the drum, it being necessary to have a certain amount of space be-
tween this bed plate and the head of the drum to provide room for the exhaust-
valve cam and its co-acting punch rods. The starboard bed plate is fastened
to the starboard head of the drum by bolts which draw the web of the bed plate
against the face of the drum. The sparking gears are driven by means of a
gear formed on a sleeve which telescopes over the hub of the starboard drum,
and has a bearing thereon, the end of the sleeve terminating in a ring which is
fastened to the crank shaft.

Since the five connecting rods must center on the one crank pin, the bronze
shoes in which they terminate can occupy only a portion of the circumference
of the pin, and with the relative proportions which here existed between the
length of stroke of crank and the length of the connecting rod, the circumfer-
ential width of the connecting-rod shoes was slightly less than sixty degrees,
thus leaving uncovered a crank space of about one-sixth of the circumference,
which it was necessary to have in order to provide room for the change in rela-
tive position of the shoes due to the angularity of the connecting rods. In

238 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

the experimental engine the connecting-rod shoes were all given their bearing
directly on the crank pin, as heretofore described, being held in contact there-
with by means of cone nuts, which were screw-threaded to the crank pin, the
taper of the cones permitting adjustment for wear. This method of connecting
these parts to the crank pin is the usual plan of connecting three or more con-
necting rods to one crank pin. So much trouble had been experienced with the
water jackets and with minor defects in the experimental engine that no long
runs had been possible with it, and consequently no trouble had been experi-
enced because of the small amount of bearing area provided by this method of
joining the connecting rods to the crank pin. When, however, the new engine
was completed it was found that after working at high power for a few min-
utes the connecting-rod shoes heated so rapidly that it was impossible to run
the engine for more than ten or twelve minutes, the excessive heating of the
shoes causing a great diminution in power besides the danger of serious dam-
age if the tests were continued longer. At first this defect seemed almost fatal,
as there appeared to be no way of providing sufficient bearing area for the five
connecting rods on one crank pin. Happily, however, the writer was able to
overcome this defect by an improved design which enables all five connecting
rods to operate on the one crank pin, and at the same time provides each with
the full amount of bearing area which it would have were it the only connect-
ing rod operating on the crank pin. This arrangement consists essentially of a
main connecting rod formed of a steel forging terminating in a sleeve which en-
circles the crank pin and is provided with a bronze lining for giving a proper bear-
ing surface between the connecting rod and the crank pin, both the steel sleeve and
the bronze lining being split, but at right angles to each other, to permit assem-
bling them on the crank pin. This steel sleeve, the upper half of which is formed
integral with the main connecting rod is rounded off to a true circle on its exterior
circumference, except at the point where the rod joins it. The other four connect-
ing rods terminating in bronze shoes are then caused to bear on the exterior of
this sleeve, being held in contact therewith, and permitted to have a sliding motion
thereon sufficient to take care of the variation in angularity of the connecting
rods, by means of the cone nuts which are screw-threaded to the sleeve and
locked thereto by means of the jam nuts, as shown in the drawings. The main
connecting rod, of course, acts in the same way as in the ordimary case where
each cylinder has its separate crank pin. The other four connecting rods de-
liver their effort to the crank pin through the sleeve in which the first connect-
ine rod terminates, and they, therefore, do not receive any of the rubbing effect
due to the rotation of the crank pin, except that of slipping a very short dis-
tance over the circumference of the sleeve during each revolution, the amount
of slipping depending on the angularity of the connecting rod. This improved
type of bearing was successful from the time of its first trial, and even in later

|
|

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 239

tests in which the engine was run for ten consecutive hours at full power it
showed no signs whatever of overheating. As this new form of connecting-rod
bearing for the crank pin had never been tried before, the precaution was taken
to leave the threads on the crank pin for the cone nuts, so that if this new
bearing should not prove successful the old plan of having the connecting-rod
shoes bear directly on the crank pin could be reverted to. These threads are
clearly seen in Plate 78 and were never removed from the crank pin, though
their removal would have added considerably to the area of the bearing sur-
face of the main connecting rod, had more bearing surface seemed necessary.

The lubrication of the main crank-shaft bearing and of the crank pin was
effected by means of a small oil cup, fastened to the port bed plate, which fed
oil through a hole in the hub of the drum to a circular groove formed in the
bronze bushing in the hub. The crank shaft being hollow, a hole was drilled
through it in line with the groove in the bushing, and the oil was then led from
the interior of the crank shaft through a pipe connected to the plug in the end
thereof, and through a hole drilled in the crank arm to the hollow crank pin.
Small holes through the crank pin permitted oil to pass to the exterior thereof
and thus oil the bearing of the main connecting rod. Small holes through the
sleeve and bushing of the main connecting rod fed oil under the shoes of the
other four connecting rods, the small holes being placed in oil grooves formed
in the interior of the bronze bushing. The lubrication of the pistons was ef-
fected by means of small crescent-shaped oil eups fastened to the outer wall
of the cylinders, which distributed the oil equidistantly around the circumfer-
ence of the pistons, through small tubes which projected through correspond-
ing holes drilled in the cylinder wall. ‘These oil cups for the cylinders were,
while small, of sufficient size to furnish a supply for approximately one hour,
and were so positioned on each cylinder as to have a eravity feed. It may be
mentioned here that while there were many parts of the engine which were
of unprecedented lightness there was nothing which excelled these oil cups in
this respect, as they were made of sheet steel .003 of an inch thick, riveted and
soldered up. The crank-shaft bearimg in the starboard drum was oiled from
an oil cup mounted on the outside of the bed plate and connected by a pipe to
a hole in the inner wall of the drum, which was connected to the oil grooves in
the bronze bushing in the hub of the drum.

The first set of pistons for this engine were similar in design to those
shown in the assembled drawings, except that they had side walls and heads
which were twice as thick as those shown. These lighter pistons were constructed
later, and were just as good as the earlier and heavier ones. It will be noted
that the pistons have two deep but thin ribs reinforcing the head. The pis-
tons were slightly tapered from the middle, where they were .005 inch smaller
than the cylinder bore, toward the outer end, where they were .0075 inch smaller

240 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE ; vou. 27

than the bore. The outer piston ring was .0035 inch narrower than its groove,
the second one .003 inch, the third .0025 inch, and the imner one .002 inch nar-
rower than its groove. The rings were bored one-sixteenth inch off center with
the exterior surface, and had one-eighth inch diameter of spring. They were
of the lap-joint type, with the sides of the laps carefully fitted and only one-
sixty-fourth-inch clearance at the ends of the laps to allow for thermal expan-
sion. As no grinding facilities were obtainable in Washington, the cylinders
were carefully bored smooth and free from taper, and the pistons were worn
in to a perfect fit by running them in by a belt for twenty-four hours, with
copious oil supply.

The main connecting rod was {-inch diameter and solid, while the other four
were of the same diameter but with a 23-inch hole in them. The gudgeon pins
in the pistons were hollow steel tubes {-inch diameter and case-hardened, and
were oiled entirely by the oil thrown off by centrifugal force from the crank-
pin bearing, the oil running along the connecting rods and through suitable holes
at the heads into oil grooves in the bronze bushings in these heads.

Since on an engine for an aerodrome the best plan for releasing the exhaust
gases from the engine is to get rid of them as soon as possible, so long as they
are released behind the aviator and do not interfere with his view in the di-
rection of motion, it was decided to have the gases exhaust immediately from
the combustion chambers; but in order to prevent their playing on and heating
the main bearing of the crank shaft in the port drum the combustion cham-
bers were each provided with a chamber below the exhaust-valve seat, with a
side outlet therefrom. The manifold pipe through which the gaseous mixture

vas supplied to the inlet valves of the engine consisted of a tube bent to a
circle and having five branch tubes, each leading to one of the automatic inlet
valves, which fitted removable cast-iron seats fastened by a nut in the upper
part of each combustion chamber. The very small amount of clearance between
the engine and the frame necessitated that this pipe be cut in three places and
joined by flanges in order to properly assemble it on the engine when the latter

yas mounted in the frame. The carburetor, which was placed near the rear of
the aviator’s car, was connected through suitable pipes to this circular inlet
pipe, at a point horizontally in line with the center of the shaft. The auxiliary
air valve consisted of a sleeve rotatably mounted on the vertical pipe leading
from the carburetor to the manifold, holes in the sleeve being brought to coin-
cide more or less with holes in the vertical pipe, by the operator, when more or
less air was required or when he wished to vary the speed of the engine. The
cooling water for the jackets of the cylinders was led to them through a circu-
lar manifold pipe on the starboard side connected by a vertical pipe with the
centrifugal pump situated at the lower point of the lower pyramid of the aero-
drome frame. The heated water was led from the jackets through another cir-

Fa

re:

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 241

cular manifold pipe on the port side, through two connections to the radiating
tubes at the front and rear, respectively, of the cross-frame. These radiating
tubes, which were provided with thin radiating ribs soldered to them, finally led
the cooled water to the tank situated in the extreme rear of the aviator’s car,
a suitable pipe from the bottom of this tank being connected to the inlet side of
the centrifugal pump. The centrifugal pump was driven by means of a verti-
cal shaft connected to the crank shaft through a set of bevel gears which drove
it at three times the speed of the engine. The bearings through which these:
gears were connected were mounted on the port bed plate, and in order to al-
low for a certain amount of vibration between the engine and the pump this
vertical connecting shaft had a. telescoping section connected through suitable
splines.

The sparking apparatus comprised, first, a primary sparker similar to the
simplest form of such devices which have since come into common use, where a
cam driven by the engine co-acts with a pawl on the end of a spring, but in
this case, as this sparker was used for all five cylinders, the cam was driven at
a speed of two and one-half times that of the engine shaft, thus making and
breaking the primary circuit five times in each two revolutions of the engine.
Second, a spark coil, the primary terminals of which were connected to the pri-
mary sparker and to a set of dry batteries. Third, a secondary distributor con-
sisting of a dise carrying a contact brush and driven at a speed one-half that
of the engine, this brush being constantly connected through a contact ring to
one of the terminals of the high-tension side of the spark coil and running over
the face of a five-section commutator, each of the sections of which was con-
nected to a spark plug, the other high-tension terminal of the spark coil being,

_of course, grounded on the engine frame. This sparking apparatus was first

constructed by using blocks of red fibre for insulation. After the engine was
completed and was being tested difficulties were met with in the sparking appa-
ratus which at that time appeared- inexplicable. After a great deal of annoy-
ance and loss of time it was finally discovered that the red fibre was not as good
an insulating medium as it was supposed to be, owing to the zinc oxide used
in making it. In damp weather the sparking apparatus absolutely refused to
work, and it was found that the moisture in the air caused the zine oxide in
the fibre to nullify its insulating qualities. This trouble, after being located,
was cured by substituting hard rubber for the red fibre.

At the time when this engine was built, as well as earlier when the experi-
mental engine was built, it was impossible to procure any wire which had been
properly insulated to withstand the high voltages necessary for the connections
between the high-tension side of the spark coil and the secondary distributor,
and from the secondary distributor to the spark plugs in the eylinders. While

at this time this appears a very simple matter, yet the trouble experienced and
27

242 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

the delays caused by the lack of such small accessories which are now so easily
procurable were very exasperating, and it was finally necessary to insulate these
wires by covering them with several thicknesses of ordinary rubber tube of
different diameters telescoped over each other.

In the early tests of this new engine, which were made with it mounted on
a special testing frame and delivering its power to the water-absorption dyna-
mometers, the engine was operated without any fly wheels, and, so far as its
~ smoothness of operation was concerned and its ability to generate its maximum
power, it did not require any.

After the completion of the tests on the testing frame the engine was as-
sembled in the aerodrome frame, which was first mounted on the floor of the
launching car. The car itself was mounted on a short track in the shop, which
arrangement provided a smoothly rolling carriage which could be utilized for
measuring the thrust of the propellers by merely attaching a spring balance be-
tween the rear of the car and a proper holding strap on the track. In the first
tests of the engine under these conditions, it was found that while the engine
itself did not require any fly wheels, yet the lack of them caused trouble with
the transmission and propeller shafts, which, while it had never been antici-
pated, was easily understood when it was encountered. This difficulty was
caused by the ‘‘ reverse torque,’’ which fluctuated from a maximum to a mini-
mum five times during each double revolution of the engine, and which set up
fluctuating torsional strains of such magnitude in the transmission and propel-
ler shafts that the shafts themselves became exceedingly hot after a few min-
utes operation of the engine, and under more prolonged periods of operation
these fluctuating torsional strains caused a permanent twisting and bending of
the shafts. The transmission and propeller shafts were at first made of tubing
one-sixteenth of an inch thick, but these were abandoned both on account of the
necessity of abandoning the screw-thread method of attaching the flange coup-
lings and gears, and also because these shafts had been designed when if was
expected to transmit only twelve horse-power to each propeller, while the in-
crease of power in the large engine necessarily required much stronger shafts.
The first shafts which were actually tested in the frame were, therefore, one
and one-half inches in diameter by three-thirty-seconds of an inch thick, the tub-
ing having been one-thirty-second of an inch larger originally and turned down
to this size to insure a straight shaft. When these shafts twisted under the
action of the reverse torque of the engine, a very much heavier set, practically
twice as thick, were constructed. When used in the tests these heavier shafts,
while much stronger, still showed a large amount of heating due to the fluctu-
ating torsional strains.

Upon ealeulation it was found that by providing specially light fly wheels
the major portion of this reverse torque could be eliminated for a less increase

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 243

in weight than would be occasioned by sufficiently increasing the thickness of
the transmission and propeller shafts to safely stand it. Since it was desired
to concentrate as much as possible of the weight of the fly wheels in the rims,
the idea at once suggested itself of building them up like a bicycle wheel by
means of tangent spokes. Two steel automobile-wheel rims were therefore pro-
cured thirty-three inches in diameter, and these were provided with tangent
spokes connected to special steel hubs fitted to the crank shaft of the engine.
The rims themselves not being quite heavy enough, and constructional reasons
necessitating their being at different distances from the center of length of the
crank pin, the extra weight which it was desired to give to these rims was pro-
vided by means of steel wire wound tightly around and fastened to the rims,
the weight of each rim being made inversely proportional to its distance from
the center of the crank pin. The first spokes which were used for these wheels
were standard bicycle spokes three-thirty-seconds of an inch in diameter, but
these were soon found to be entirely too weak to withstand the sudden strains
due to the rapid starting of the engine. They were therefore replaced by stand-
ard spokes one-eighth of an inch in diameter, but these also proved too weak
and were later replaced with special spokes made in the shop out of No. 10
coppered-steel wire, which by test was found to have a tensional strength of
2192 pounds. As these steel rims were only one-sixteenth of an inch thick and
had not been made exactly true, but had been straightened before being used,
it was found that they very quickly went out of shape under the strain due to
the centrifugal force at high speeds, and also when the engine was suddenly ac-
celerated. As long as they did stay true, however, it was found that they were
sufficiently heavy to provide all of the fly-wheel effect it was necessary to have
in order to eliminate all trouble from the reverse torque.

After further consideration, it was decided that the only means of con-
structing a fly wheel which would have a stiff rim and at the same time would
not be heavier than the steel ones, which had been found adequate, was by per-
petrating what would at first sight appear to be an absurdity. A new set of
rims for the fly wheels was made by constructing them of an aluminum ecast-
ing, the section of the rim being U-shaped. After machining these rims and
assembling the fly wheels with them, it was found that they were many times
stiffer than the previous steel ones of the same weight, and after this change no
further trouble was experienced in keeping the fly wheels perfectly true, even
under the most severe strains. In fact, on one occasion when the engine broke
loose from the propellers, it ran to a speed, which, while not exactly known,
yet reached the limit of the tachometer, which was 2000 R. P. M., without in-
jury to the fly wheels.

Tt will be recalled that in starting up the engine on the quarter-size model,
the initial ‘‘ cranking ’’ necessary with a gasoline engine was accomplished by

244 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

having two of the mechanics turn the propellers. While this same plan might
have been followed in the case of the large aerodrome, yet it would have in-
volved some danger to the mechanics and would also have left the aviator with-
out any means of restarting the engine should it for any reason stop while in
the air. Believing it to be very important to provide means for enabling the
aviator to restart the engine in case it stopped in the air, the writer devised
the starting mechanism shown in the drawings, Plates 78 to 80. Fastened by
tongues and grooves to the port side of the engine crank shaft, just outside of
the bed plate, is a worm wheel, on the hub of which is mounted the bevel gear
which drives the water-cireulation pump through the bevel pinion, as already
described. Mounted on the web of the bed plate are two brackets, in which
the shaft for the starting crank is journaled, this shaft passing forward and
downward through the front of the cross-frame of the aerodrome, where it is
journaled in a bracket secured to the brace tubes thereof. At the front or lower
end of the shaft a crank handle is connected thereto by a ratchet mechanism.
The upper end of the starting shaft, between the bearings of the two support-
ting brackets, is tongued and grooved, and slidably mounted thereon with co-
acting grooves and tongues is a worm screw which, in the position shown in
Plates 79 and 80, is in gear with the worm wheel just described. However,
when the worm screw is slid along on the shaft until it is against the upper
bracket it is out of gear with the worm wheel. Mounted in the interior of the
tubular starting shaft is a spring-pressed pawl plug, not shown, but which pro-
jects through one of the tongues on the shaft near the upper bracket. If the
worm screw is slid up against this upper bracket, this pawl catches in a radial
hole in the worm screw and holds it in this position out of gear with the worm
wheel. Connected to this pawl plug and passing longitudimally through the cen-
ter of the shaft is a wire which terminates in a button just at the end thereof.
By pulling on this button the operator may release the worm and thus permit
it to slide downward so that when the starting crank is turned in a clockwise
direction the worm will screw itself into gear with the worm wheel, and any
further turning of the starting crank will cause the worm to force the worm
wheel, and, consequently, the engine shaft, around ina clockwise direction. As
soon as the engine gets an explosion the worm wheel slides the worm along
against the upper bracket, where the spring pawl catches and holds it till it
is again released by the operator as before.

This starting mechanism was a success from the first, and the engine was
never started up in any other way. With an aerodrome having the qualities of
automatie equilibrium, which the Langley machines have, it was felt very cer-
tain that by this mechanism the engine could be easily restarted while in the
air, in case it was inadvertently stopped.

wo. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 245

The reason for building the engine with five cylinders instead of some other
number, and for arranging them radially on a central drum using only one crank
pin may not appear quite obvious. The advantages gained by such a construec-
tion, however, are very great, and may be briefly summed up as follows:

First, since in a gas engine of the four-cycle type there is only one explo-
sion in each eylinder every two revolutions, and the crank shaft and crank pin
therefore are loaded only one-quarter of the time for each cylinder, it is obvious
that by having four cylinders arranged radially around a central drum the
load on the bearings of a single crank shaft and crank pin may be kept very
uniform. However, with four cylinders thas arranged it is impossible to have
the cylinders explode and exert their effort on the crank at uniform intervals
in the eycle, it being necessary to have the cylinders explode in the order of
1, 3, 4, 2, 1, ete., thus giving intervals between explosions of 180 degrees, 90 de-
grees, 180 degrees, 270 degrees, ete., or to have them explode in the order of 1,
3, 2, 4, 1, ete., thus giving intervals of 180 degrees, 270 degrees, 180 degrees, 90
degrees, ete. On the other hand, with any odd number of eylinders the explo-
sions will oceur at equal intervals in the cycle. With three cylinders they will
explode in the order of 1, 3, 2, 1, ete., or at equal intervals of 240 degrees,
while with five cylinders they will explode in the order of 1, 3, 5, 2, 4, 1, ete.,
or at equal intervals of 144 degrees. It is therefore seen that there is a great
advantage in smoothness of operation and uniformity of torque of the engine
through having an odd number of cylinders instead of an even number.

Second, it is readily apparent that the greater the number of cylinders,
provided the number is an odd one, the more uniform the torque will be, and
it would seem at first that seven cylinders would therefore be better than five,
since the uniform intervals between explosions with seven cylinders would be
only 103 degrees (approximately). The advantage gained, however, through
seven cylinders instead of five is largely, if not completely, counterbalanced by
the added number of parts and the difficulty of providing sufficient cireumter-
encial width for the econnecting-rod shoes on the crank-pin bearing, even with
the improved construction of this bearing already described. There is consid-
erable fluctuation of the torque in each revolution of the engine with five eylin-
ders, but this fluctuation of torque is more easily smoothed out by the use of
very light fly wheels than by increasing the number of cylinders, and thus
adding to the complication of the engine.

Third, the strongest point in favor of the radially arranged cylinders is the
reduction in weight and complication which it permits. The crank shaft is re-
duced to the very minimum, there being only one crank pin with two main
bearings which ean, without any difficulty whatever, be kept absolutely in line
with each other and thus prevent binding and loss of power. Again, the use
of a single-throw crank not only reduces the cost and weight of the crank it-

246 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL, 27

self, but makes it very much less liable to damage; long crank shafts with sev-
eral crank pins being frequently twisted by improper explosions in the eylin-
ders. The supporting drum or crank chamber is likewise reduced to the very
minimum, both in weight and simplicity, the drums being perfectly symmetrical
with no lost space either inside of them or on their exteriors. The cam mech-
anism for operating the valves is reduced to a simple ring carrying (for a five-
cylinder engine) a double-pointed cam and journaled on the exterior of the hub
of one of the drums, the cam being driven by a train of gears journaled on studs
mounted on the drum, and co-acting with a gear fastened to the erank shaft
against the crank arm.

The radial arrangement of the cylinders is thus seen to give not only an
engine with the smallest number of parts, each of which is as far as possible
worked to a uniform amount during each complete revolution of the crank shaft,
but it also gives a very compact and readily accessible mechanism with its cen-
ter of gravity coincident with its center of figure, and with the liability of dam-
age to if, in case of a smash of the vehicle on which it is used, reduced to the
minimum from the fact that the greatest weight is located at the strongest part.

Fourth, and of almost as great importance as the reduction in weight which
the five-cylinder radial arrangement permits, is its unusual qualities as regards
vibration. Since these five-cylinder engines were built by the writer a very
thorough treatment of their properties as regards balancing has been given in
a treatise on the balancing of engines,’ so no discussion of the mathematical
formule involved in a study of the question of the inherent balancing proper-
ties of these engines will be here given. It is sufficient to call attention to the
fact that in an engine having five cylinders arranged radially, all of the recip-
rocating parts are balanced for all forces of the first, second and third orders.
As it is only the reciprocating parts which give any trouble in balancing any
engine, the unbalanced rotating parts being readily balanced by placing an equal
weight at an equal distance from the center of rotation, and on the opposite
side thereof, it is readily seen that the properties of balancing which are in-
herent in this type of engine are unusual. <A six-cylinder engine having a six-
throw crank shaft is not nearly so thoroughly balanced as this type having its
five cylinders radially arranged, for in the latter case all the moving parts are
in one plane, while in the former case the moving parts are in six separate and
parallel planes, and there is consequently considerable longitudinal vibration
which can never be overcome. While this is true as regards the vibration due
to moving masses, it is still more impressively true as regards vibration due
to reaction arising from the force of the explosions in the engine eylinders, espe-
cially when the engine is running slowly and having heavy explosions.

The usual practice in balancing the rotating parts of an engine is to attach

‘See Balancing of Bngines, by Archibald Sharpe.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 247

balance weights to the crank arms which are prolonged beyond the center of
the crank shaft and on the opposite side from the crank pin; the radius of rota-
tion of these balance weights being made approximately equal to the radius of
the crank pin. But aside from the co istructional difficulties which would be
introduced, it was seen that if this plan was followed in this engine it would
require a very large additional weight. Since the amount of this weight could
be diminished in exact proportion to the increase of the radius of rotation of
the balance weights, it was at first decided to attach the weights to the rims
of the fly wheels, the relative amount of weight attached to e: ach wheel being
inversely proportional to its actual longitudinal distance from the erank-pin
center. It was very soon found that the attachment of these balance weights
to the fly wheel caused excessive strains on the rims of the wheels, thereby
causing them to go out of line. In order, therefore, to keep the amount of bal-
ance weight small by carrying it at a considerable distance from the center of
the shaft, the weights were finally arranged as clearly shown in the drawings,
Plates 78 to 80. There it is seen that the main portion of each of the balance
weights consists of a flat arm bolted between the flanges which couple the trans-
mission shafts to the engine shafts. The flat arm terminates in a lozenge-shaped
lug, additional weight being provided by a plate fastened to one end of a tube,
the other end of which terminates in a collar fastened around the transmis-
sion shaft. The tube is inclined at an angle of about thirty degrees with the
flat balance arm, thus acting as a brace to prevent the balance arm from wob-
bling, the plate on the bracing tube beimg fastened to the lozenge-shaped lug
by means of small bolts.

The tabulated statement of the weight of this large engine is given below.
From this it will be readily seen that the net weight of the engine proper 1s
124.17 pounds. The fly wheels were in no way necessary to the engine itself,
but were used solely for the purpose of smoothing out the torque of the engine
so that the transmission shafts and propeller shafts might be kept down to the
very minimum in weight. Including the two fly wheels, the weight is 140 pounds.

Including the 20 pounds of cooling water the total weight of the power
plant is 207.47 pounds. W ithout flywheels the total weight is 191 .64 pounds.

The construction of this large engine was completed in December, 1901,
and the first tests of it were made in January, 1902. As already stated, these
first tests were made with the engine mounted on as special testing frame and
delivering its power to two water- absorption dynamometers, no fly wheels be-
ing used, as none were required. Later, when it became necessary either to
use fly wheels or to greatly imcrease the weight of the transmission and pro-
peller shafts, in order to overcome the reverse torque, the two light fly wheels
were added, and another series of tests was made of the engine on its testing
frame. The arrangement of the engine, dynamometers, and accessory appa-

248 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

ratus is clearly shown in Plates 82, 83 and 84. The engine ran in a clockwise
direction, as viewed in Plate 82. AA are the fly wheels; BB the balance weights ;
CC the dynamometer shafts, on which are fastened the rotor plates which re-
volve inside of the dynamometer drums, DD, between stator plates fastened
therein. The drums have a hub on either side, by which they are supported,
these hubs being journaled on ball-bearings in the pedestals resting on the
wooden framework. The rotor plates do not touch the stator plates in the dyn-
amometers, but drag on the water with which the drums are partially filled,
and thus tend to cause the drums to revolve around with them. The torque on
each drum is measured by means of a rope, not shown, fastened into the hook
at the top of the drum, the rope being given a partial coil around the drum and
passing off tangent thereto at the horizontal diameter is fastened to a pair of
spring scales hung from the ceiling vertically above the point of tangency. The
scales and ropes were unfortunately not in position when these photographs
were taken, but the arrangement of them should be readily understood. As the
friction of the rotor plates on the water heats it in exact proportion to the
amount of power absorbed, the small amount of water in the drums would be
soon converted into steam unless continually renewed or cooled. When the rotor
plates are revolving the centrifugal force keeps the water pressed toward the
circumference of the drum, and the friction at any speed is dependent on the
area of the rotor plates in contact with the water. The horse-power required
to revolve the plates at any definite speed can therefore be controlled by hav-
ing an outlet for the water at the proper radial distance from the shaft. The
water from the water mains is led through the upper vertical pipe and allowed
to flow into the funnel, and thence into the drum near the center where the cen-
trifugal force throws it to the circumference of the drum. The lower vertical
pipe is connected to the drum at a suitable radial distance from the center, and
the heated water thus passes through this pipe and into the lower funnel con-
nected to the sewer. By the use of the funnels the drums are allowed to rock
sufficiently to exert their pull on the spring scales without being affected by the
supply and exhaust of water.

The water for cooling the cylinders is led from the bottom of the tank E
to the circulating pump F, supported in a discarded lower pyramid of the aero-
drome frame, the pump being driven by the small vertical shaft, as already
described. The water, after passing through the pump and the engine cylin-
ders, is led back to the upper part of the tank. By suitable connections to the
water mains and sewer, the water in the tank is kept at any desired tempera-
ture. The gasoline supply tank is seen on the left-hand side of the testing
frame, as viewed in Plate 82, the carburetor being placed below it and the gas
supply pipe from the carburetor passing through the gasoline tank. Instead of
jacketing the carburetor, a grid formed of thin copper tubes is supported just
above the multitude of small air pipes leading into the carburetor, and some of

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL, 27, NO. 3, PL. 82

igi SA

DYNAMOMETER TESTS OF LARGE ENGINE

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

VOL, 27, NO. 3, PL. 83

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DYNAMOMETER TESTS OF LARGE ENGINE

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 84

DYNAMOMETER TESTS OF LARGE ENGINE

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 249

the hot water from the engine is by-passed through this grid and thus warms
the air as it passes into the carburetor. The smal! pipe that by-passes this
water through the grid is seen connected to the outlet water pipe just above
the cylinders, a small butterfly valve in the outlet pipe enabling the amount of
heated water passing through the grid to be controlled. The return from the
grid is by means of the small pipe leading to the top of the large water tank.
The tachometer, which gives instantaneous readings of the speed of the engine,
is seen at G, where it is at all times in full view of the operator.

These dynamometers proved to be excellently suited for the testing work,
and far ahead of anything else the writer has ever found for engine testing.
Since the power required to rotate the rotor plates, with a uniform amount
of water in the drums, varies as the cube of the speed, it is readily seen that it
is impossible for the engine to race or injure itself by running away, as fre-
quently happens where there is no engine governor and Prony brakes are used
to measure the power.

In the early tests the engine was never allowed to develop more than 40
horse-power, as it was feared that by letting it develop more, which it was
clearly seen to be capable of, it might be injured and cause a delay in the tests
of the aerodrome. In the second series of tests it was allowed to develop 51
horse-power at 935 R. P.M., but it was not thought to be advisable to let if run
at maximum power for more than an hour, for the same reason as before. In
the summer of 1904, after it was seen that there was no immediate possibility of
securing funds for continuing the tests of the aerodrome, it was planned to
enter the engine in the competitive tests at the St. Louis Exposition, where a
prize of $2500 was offered for the lightest engine for its power. As the condi-
tions specified in this competition required that the engine run at its maximum
power for one hour, and that this be followed by a durability test of ten hours’
continuous running, it was decided to make some durability tests of the engine
before taking it to St. Louis. In these tests, the engine was run on three sepa-
rate trials for a period of ten hours? with a constant load of 52.4 horse-power
at 950 R. P.M. Even in these long durability tests the engine and the dyna-
mometers both worked so smoothly and evenly that the engine did not vary its
speed more than ten revolutions per minute, and the pull on the spring scales
varied less than ten pounds in the entire ten hours. Considerable correspond-
ence was had with the officials of the St. Louis Exposition regarding the en-
trance of the engine in the competition, in order to make sure that suitable
facilities for conducting the tests had been provided. After receiving assurance
that everything necessary had been provided, the engine and its testing dyna-
mometers were boxed for shipment to St. Louis and arrangements were just
being completed for their transportation when the following telegram was re-

1xcept for a ten minute stop to renew the supply of lubricatine oi] and change the sparking
batteries.

250 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

ceived from the director in charge of the aeronautical department of the Ex-
position: ‘‘ On account of lack of competition engine tests abandoned.’’? As
the main object of entering the engine in the competition was to insure for it
an unquestioned record of its performance it was decided to reassemble it in
the testing frame in Washington and invite some engineers of prominence to
witness and certify to its performance, but on account of the lack of funds for
meeting the expenses incident to such a series of tests as it was planned to
make this was never done.

In the tests which were witnessed on April 26, 1902, by Captain I. N. Lewis,
Recorder of the Board of Ordnance and Fortification, the engine was held down
to a pull of 200 pounds on a 13-inch lever, when running at 1000 revolutions per
minute. In the later tests in May, 1903, which were witnessed by Captain Gib-
son, who was then Recorder of the Board of Ordnance and Fortification, and
Mr. G. H. Powell, the Secretary of the Board, the engine was allowed to work
at a pull of 265 pounds on the 13-inch lever arm at a speed of 950 revolutions
per minute. In the tests made in August, 1904, the engine was run for ten con-
secutive hours‘ at a pull which varied from 263 to 271 pounds, or an average of
267 pounds, on a 13-inch lever, with the speed varying from 945 to 955 revolutions
per minute, thus showing 52.4 horse-power at the average speed of 950 R. P. M.

DETAILED WEIGHT OF NEw LARGE ENGINE.

Name of part. . Weight in grammes.
Gram esheaht, Soir crepsteretrts arararstaceletots teoverstere terial ateicteie)aletelslefal-taust-retetevekereretektere 5,225
Connecting s rods (coral) eeietecietereciettatcteiieievetel teeters ote loteietetei teri traieaetate 5,005
PIStOniS— Noi dvacrrc ocheiets ore atete ake orauar ote aetarert area rercleteye) cicheticetersieletetakeiaietars 1,652

INO Fp2) race aleve craic ctarevalecstaiais cet stoks ,sestels chs to yecs) aye tetetatayafogehetalorsyslovene eects 1,647

INO 203. pater ciese Srohclevere avetararalo re rovetecste rater cbereiaiots otclahetelevelet ckeketersiavearerets 1,655

IN (iy Ges Sap odow boo de Hobrt en osOm Codon uocaDbo od sOuCORg so 1,660

IN foLaa Te ticto dito ond de ousic dete Geir cae nodadooboboson nop sodce 1,646

Cylinders—No. 1 (including exhaust and inlet valves, oil cups, etc.)... 4,768

No. 2 (including exhaust and inlet valves, oil cups, etc.)... 4,685

No. 3 (including exhaust and inlet valves, oil cups, ete.)... 4,638

No. 4 (including exhaust and inlet valves, oil cups, ete.)... 4,637

No. 5 (including exhaust and inlet valves, oil cups, etc.)... 4,796

Port crank chamber drum, including cam, cam gears, punch rods, ete.. 5,225

Starboard crank Chamber Gnummtic es rctetern cheretsrey-ioletetol a\clerefoleleloy> eleinleintelel=) i> 3,440

Sparks plies ((5)) ye cpaten voters alate talepe ctetete eketetetoye) teasietehst=untatel fel Relstalot ate oe raiaiel gate 450

Outlet Sweater apipeser circ crsclerseteetepe teeta oetel el alien elo lelebetstol ela leieiiatalafelsi otra) 450

Imlet water pipe ciiecicyetoicveselctoie siete eteletetolokel seve tavelereveioi=l-/alalelohstaletaliell<list=or> 360

Inlet easimamifol dls nfercse crete oe ele ce eyaveteucesl al toieteke ou tes eis see lst hnlist oferoisy vlcteks]otst= 1,700

Primary and secondary sparkers and WireS............+..+++e2+-+0+- 512

Balance arm with braces for same—starboard ...................+- 1,040

Balance arm with braces for Same—port .........--eeeee eee ceevees 1,067
Total) pency. dass co cresararierctorereie oie heater alenetet eats cteletoneletatero te 56,323 = 124.17 Ibs.

Starboard tly, wheels ctemrecitatisratertersistas, lelorctstelstaranelotctetetal Mela [ste lobe ietat-iatays 3,946

Portiflys wheel oars etree iets erete vera ato lon eerie cele wheratis ol effet oko lotelenaie paral Natatatets 3,234
Total weight of engine and fly wheels............-- 63,503 = 140.00 Ibs.

Spark coil and batteries. ............-.2 2. secre cree reece renee en eres 6,800

Carburetor oiisisc ceo hc ole Seles ele ates we snes aun taley fate lehete vee etpiota atm arstatete 3,751

Inlet gas pipe from carburetor to manifold..............-0-+2++-+-- 756

Gasoline CAMS ere sreceie eerete elereresaeteler al aetersietn cfoleye cohelwieeonehcereheleYehstscursistsl Pate 1,004

Water: Camic. is ccc area coke eich ioveisceteteraiotetaval iatalolebolateaatcel ote ske-steveleratsiel ae 717

Water circulating pump and shaft...............-.sscercseeceessces 807

RAGGA bON | ive sis oc cya eietetena ote sala aver acctalioke =) avatar eal cale Ielainle delete whajefoeuielaloioly lene 7,700
Total weight of power plant...............-..-..--- 85,038 = 187.47 Ibs.

1See foot-note, page 249

CHAPTER XI
SHOP TESTS OF THE AERODROME

In June, 1902, after the proper adjustments of the carburetor and other
accessories of the engine had been accurately determined in the tests on the test-
ing frame, the engine was assembled in its proper position in the aerodrome
frame and connected to the propellers. The aerodrome frame was then mounted
directly on the floor of the launching car, which was placed on a short track
laid on the floor of the shop, as previously described. A large spring balance,
which had been previously calibrated, was then connected between the car and
an upright fastened to the track, and tests were made to determine the thrust
developed when the engine drove the propellers at different speeds. Upon find-
ing that there was comparatively little vibration when the engine was driving
the propellers even at its maximum speed, it was felt safe to raise the aero-
drome from the floor of the ear and place it upon the uprights on which it would
be supported in launching it. Quite an extended series of tests was then
made, and although the uprights raised the aerodrome frame until the midrod
was practically 9 feet from the floor of the car, and in the tests at maximum
power the propellers developed an average thrust of 450 pounds, yet it was
found that the clutch hook held the bearing points of the frame so securely on
the uprights of the car that all fear that the aerodrome might break loose from
the car during the launching process was removed.

Upon the completion of these tests, which had proved most satisfactory,
the aerodrome frame was supported from the ceiling of the shop by means of
four short coil springs which reproduced as nearly as possible the elastic or
flexible suspension which the aerodrome would have when supported by its
wings in the air. These springs were attached at the same points on the
main frame of the aerodrome at which the wings would be attached, thus per-
mitting a careful study of the amount of flexure and vibration which it would
undergo in actual flight. The most remarkable difference in the nature of the
vibration induced in the frame was found when the aerodrome was thus
supported by springs. When it was supported on the rather unyielding launch-
ing car, the general tremor set up in the frame by the engine and propellers
was, while small, yet harsh, the effect on a person standing in the aviator’s car
being rather unpleasant in the joints of the knees when experienced for several
minutes. When the frame was suspended by the springs it was found that all
this harshness of tremor disappeared, it being replaced by a slight general and
rapid tremor of the whole frame, which was not at all unpleasant, and which

251

202 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27
had no tiring effect on one standing in the aviator’s car. In fact, the vibration
in the first case resembled rather closely that of a motor vehicle supported on
wheels having metal tires, and in the second case a motor vehicle supported on
wheels having pneumatic tires.

As in these tests in the shop it was impossible to keep the engine cool by
circulating its cooling water through the radiator, since there was no air ecur-
rent blowing across the latter to carry away the heat, it was necessary to con-
nect an extra water tank in the cooling-water cireuit. A tank holding about ten
gallons was used, and this sufficed for about ten minutes before the water was
raised to the boiling point.

During one of these tests when the frame was supported from the springs,
and while the engine was developing about fifty horse-power, without any warn-
ing whatever, both propellers suddenly twisted off from the flanges by which
they were connected to the propeller shafts, thus leaving the engine entirely un-
loaded. The propellers both dropped quietly to the floor, making only about
one or two turns in falling the distance of approximately 10 feet, and the en-
gine, which had been running at about 850 R. P. M., immediately speeded up
to an exceedingly high speed, which, while not exactly known, since the tachom-
eter only read to 2000 R. P. M., yet from the deflection produced on the tachom-
eter needle must have been considerably higher than this. Although the fly wheels,
which were 33 inches in diameter, with the aluminum rims and wire spokes,
had been exceedingly well made, yet it was not considered safe to run them
at this speed, and the engine was immediately shut down. At the moment, how-
ever, that the engine had broken loose from its propellers and also momentarily
jumped to this exceedingly high speed there was absolutely no vibration that
could be noticed, the unloaded engine running as smoothly as an electric motor.
This showed very clearly that the running balance of the engine was as near
perfect as it would be possible to get it, except with a seven-cylinder engine,
which is theoretically capable of more perfect balance. It was evident that what
small vibration there was in the frame while the engine was developing its
power was due almost entirely to the reverse torque, and, of course, could never
be entirely eliminated.

In the tests of the engine working in the frame, both while mounted on the
ear and also when suspended from the springs, a great amount of delay was
caused from the fact that the ball-bearings on the transmission and propeller
shafts frequently went to pieces. There were two reasons for this: In the first
place, although carefully selected balls were used, defective ones were continu-
ally encountered. Even a slight defect in a single ball resulted in its breaking
under the rather severe test to which they were subjected, and, as is well known,
the breaking of one ball in a ball-bearing usually results in the destruction of
especially if the races are light. The second cause was that

the whole bearing

5)

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 253

the whole aerodrome had been originally designed with the expectation of using
a maximum of 24 horse-power, and as no margin had been left to provide for
possible increases in the size of the bearings, there was no room to permit them
to be increased without almost completely reconstructing portions of the trans-
verse frame. While in the end it would have been cheaper to have reconstructed
these portions in order to put in larger bearings, yet, as is always the case in
experimental work of this kind, small changes which seem to hold out hope of
overcoming difficulties are usually followed, rather than reconstructions which
ean be seen to involve considerable expense and delay. After a number of minor
changes had been made in the bearings, they were finally able to stand up fairly
well under the severe strain to which they were subjected when the engine de-
veloped its full power, and no further changes were made in them; a defective
race being, however, replaced by a new one as 0¢ -asion demanded.

These tests demonstrated very clearly that at speeds of approximately 1000
revolutions per minute ball-bearings which are subjected to considerable loads
should be calculated with a considerable margin of safety, as the yielding of
the frame, which must necessarily be far from rigid, causes more or less error
in the alignment of the shafts and bearings, and this introduces considerably
increased strains on the bearings. In the early tests before the bearings were
strengthened, the balls in some of the races were on a few occasions ground to
a very fine powder before it was discovered that they had failed. Such a result,
it will be understood, could and did occur in the course of a very minute length
of time.

In imitating as nearly as possible the conditions to which the carburetor
of the engine would be subjected during the period of launching, numerous tests
were made in which the engine was brought to its maximum speed and, without
changing the adjustment of the mixture-controlling devices of the carburetor,
sudden blasts of air were turned on it from various directions, and these were
continued until the mixture-control devices were perfected to such a point that
gusts of thirty miles an hour suddenly directed from any point against any
portion of the apparatus would in no way effect the speed and power of the en-
gine. These tests were considered necessary in view of the very sudden changes
in conditions to which the aerodrome would be subjected during its brief run
down the launching track, the conditions changing in approximately three sec-
onds from absolute quiescence of the aerodrome to a plunge through space at
thirty-five feet per second. An aviator would be more than oceupied with main-
taining control of himself and of the aerodrome, which at the moment of leaving
the track might require considerable change in the adjustment of the Pénaud
tail, and he would, therefore, not be able to make any adjustments of the engine-
control devices. This supposition was entirely confirmed in the actual tests of
the aerodrome which are to be later described, the rush down the track being

254 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

so very brief that the engine could not have been given any attention by the
aviator had it needed it, which fortunately it did not.

It is hardly necessary to recount at any length the great difficulties which
were experienced in these tests of the engine in the aerodrome frame before
the shafts, bearings, propellers, and, in fact, the frame itself were all properly
co-ordinated so that confidence could be felt that all of the parts would stand
the strains which were likely to come on them when the aerodrome was in flight.
These tests were really not tests of the engine itself, but of the frame, shafts,
and bearings. Suffice it to say that nearly a year was consumed by the various
breakages of the shafts, bearings, and propellers before it was felt that all of
these parts could be depended on, and even then the weakness of the bearings
above referred to was fully recognized. Had some of the better-grade balls
and steels for the bearings, which have since that time come on the market,
been obtainable then, there would have been no difficulty with these bearings.
However, this same remark might be made with reference to nearly all of the
details of the aerodrome, for it was the accessories, such as bearings for the
transmission and propeller shafts, spark plugs, coils, batteries, and a suitable
carburetor for the engine, that caused the chief delay after the main difficulty
of getting a suitable engine had been overcome.

CHAPTER XII
FIELD-TRIALS IN 1903

The extended series of shop tests which had oceupied a considerable por-
tion of the late winter and early spring of 1903 had demonstrated the following
facts: First, with the aerodrome mounted on the launching car, a propeller
thrust of from 450 to 475 pounds could be maintained indefinitely by the en-
gine, and even when the engine was delivering its full power to the propellers,
the vibration was so small as to cause no apprehension that the wings and rud-
der would be made to vibrate sufficiently to produce undue strains in them.
Second, with the aerodrome suspended from the ceiling by springs at the points
at which the wines would be attached, the vibration produced by the engine de-
veloping its full power was even less than when the machine was mounted on
the launching car, and there was, consequently, even less cause for concern that
the wings and rudder might be set im vibration when the machine was free in
the air. Third, the engine could be depended upon to deliver something over
52 horse-power when the five cylinders were working properly, and even with
one cylinder not working, but acting as a dead load against the others, approx-
imately 35 horse-power could be developed, while with two cylinders not work-
ing at all, the three which were working would deliver about 25 horse-power.
Therefore, even assuming that two of the five cylinders might become deranged
during a flight, there should still be sufficient power to propel the machine.
These tests, some of which had been witnessed by members of the Board of
Ordnance and Fortification, clearly demonstrated that the time had arrived when
it was safe to give the aerodrome a test in free flight. The machine itself, to-
gether with all its appurtenances and much extra material for repairs in case
of breakages, which previous experience had shown to be almost certain, was
accordingly taken from the shop and placed on the house-boat preparatory to
taking it down the river to the point opposite Widewater, Va., which had al-
ready been selected as the “ experimental ground.”’

Owing to the limited size of the shops it had been impossible to place the
wings and rudder in their proper positions on the aerodrome and determine its
balancing in a way similar to that practiced with the models. The approximate
settings for the wings and rudder had, however, been determined by caleula-
tion from the data obtained in the test of the quarter-size model, so that it re-
mained only to place the wings and a weight to represent the rudder actually
on the machine in the large space of the house-boat (which, however, was not
large enough to permit the rudder to be assembled along with the wings), and
thus check the balancing previously determined by calculation. There were very

255

256 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE you. 27

few appurtenances which could be shifted in balancing the aerodrome, but the
proper disposition of weight had been so accurately determined by calculation
that the floats, which, as will be seen from the various photographs, were merely
eylindrical tanks with pointed ends, and of a sufficient capacity to cause a dis-
placement great enough to float the aerodrome when it came down into the water,
proved sufficient ballast for shifting the center of gravity to its proper point.
The flying weight of the aerodrome was 830 pounds,’ including the weight of the
writer, which was 125 pounds. The total area of the wings or supporting sur-
faces was 1040 square feet, or the ratio of supporting surface to weight was
1.25 square feet per pound, which is the same as .8 pound per square foot.

After the balancing of the large aerodrome had been completed on the
house-boat, and everything else got in readiness as far as could be done before
actually arriving at the point at which the test was to be made, the house-boat
was towed down the river on July 14, 1903, and fastened to its mooring buoy,
which had been placed in the middle of the river at a point practically opposite
Widewater, Va., and approximately forty miles from Washington. See Coast-
Survey Chart, Plate 85.

Sleeping quarters for the force of eight workmen and the regular soldier
from the United States Army, who had been detailed as a special guard, had
been provided on the boat, but owing to the lack of space it had been found im-
practicable to arrange proper cooking facilities on the boat, and it had been
found necessary to arrange to transport the workmen to Chopawamsic Island,
near Quantico, Va., for their meals. It had been planned to use the twenty-
five-foot power launch for this purpose, but owing to the heavy storms which
became quite frequent soon after the house-boat was taken down the river, it
was found that the small launch was not sufficient, and it was necessary to
employ a tug-boat and keep it stationed there at all times. This added very
considerably to the expense of the experiments, as the hire of this one tug-
boat very nearly equalled the pay-roll of the workmen, and while it was not
expected that the stay down the river would be so greatly prolonged as after-
wards proved the case it was felt certain that mmor delays were sure to occur
and the experiments would at the very least require several weeks.

Had it been possible to foresee the great delay which finally occurred be-
fore the large aerodrome was actually launched, and the great expense arising
from the necessity of maintaining one or more expensive tug-boats constantly,
it is very certain that an experimental station nearer Washington would have
been selected, even though the nearer places on the river which were available
were much less suitable, both on account of the river being much narrower and
the traffie very much heavier. In fact, at the time that the house-boat was taken
down the river on July 14, with the expectation that the experiments with the

The weight was afterwards increased to 850 pounds due to repairing the wings and adding more
sparking batteries.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 85
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1882 SCALE 1 116 INCH TO STATUTE MILE

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no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT PASIT

large aerodrome would certainly be concluded within four weeks, the expenses
of the work, which had been met from the Hodgkins Fund of the Smithsonian
Institution since the original allotment from the Board of Ordnance and Forti-
fication was exhausted more than a year previously, had already made such
heavy drafts on this fund that Mr. Langley was most reluctant to draw further
on it, even to the extent which seemed necessary to meet the expenses of a
month of ‘‘ field-work.’’

Before making the tests of the large aerodrome, it was intended to give
the quarter-size model a preliminary trial to test the balancing which it was
proposed to use on the large machine. For this test it was planned to employ
the small launching apparatus mounted on top of the small house-boat, which
had been used in the experiments with the steam-driven models Nos. 5 and 6
in 1899, and later with the quarter-size model in 1901. However, after arriv-
ing down the river, it was found that the small house-boat which had been
anchored at Chopawamsic Island since the experiments in 1901 had deteriorated
to such an extent that it was unsafe to take it out into the river. The launching
apparatus for the model was, therefore, removed from it and placed on the turn-
table of the large house-boat, alongside the launching track for the large ma-
chine. After completing this transfer of the model-launching apparatus every-
thing was thought to be in readiness for a test of the quarter-size model, but
upon making a shop test of the model to make sure that its engine was work-
ing properly, it was found impossible to get it to work at all. A few explosions
eould be obtained once in a while, but very irregularly. After spending consid-
erable time in trying to locate the difficulty, it was found that the commutator
which distributes the high-tension sparking current to the proper cylinder at
the proper time was short-circuited. This commutator had been made of ‘‘ in-
sulating fibre ’’? and had never caused any previous trouble. It was now found,
however, that the very damp atmosphere which had been experienced during
the preceding two weeks, when the fog for a large portion of the time was so
heavy that objects at a short distance across the water could not be seen, had
caused the moisture to penetrate the fibre and thus destroy its insulating qual-
ities. After much trouble some vulcanite and mica were secured and a new com-
mutator made to replace the fibre one, and, then, after some minor difficulties
had been remedied, the engine for the model was got into good condition again.
After getting satisfactory shop tests on the model aerodrome, and having every-
thing in readiness for a flight, it was necessary to wait many days before the
weather was calm enough for a test. However, on August 8 the weather quieted
down and the model was launched at 9.30 a.m. into a wind blowing about 12
miles per hour from EH. SE.

Referring to Plate 86, which shows the quarter-size model mounted on its

launching car on top of the large house-boat, and which was taken only a few
28

258 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

minutes before the model was actually launched, it will be noted that a board
(A) projects from the front of the launching car. This board, which is mounted
in a false floor of the launching car, is so arranged that when it strikes the two
blocks (B) at the end of the track it is driven backward in the car against the
triggers which prevent the uprights (D), supporting the aerodrome, from being
folded down against the floor. When this board strikes the triggers it releases
them and the springs (C), which in this case were rubber bands, immediately
fold the vertical posts or uprights (D) against the brace posts (#), which are
immediately folded down flat against the floor of the car through the action of
the spring hinges, by which they are connected to it. These uprights (D),
which support the aerodrome at the front and rear, respectively, are not re-
leased until a fraction of a second after the release of the clutch hook (F),
which is attached to the middle upright (G), and which, grasping the lower
pyramid, holds the machine down firmly against the uprights (D) previously
referred to. In order to prevent the possibility of the aerodrome being re-
leased prematurely while the car is held at the extreme rear end of the track
by the hook (H), a steel pin (J), which can just be seen in the photograph, is
pushed through a hole in the board (4), and into a hole in a cross-member on
the bottom of the car, thus holding the board in its proper position. After the
engine is started up one of the mechanics who has assisted in starting it is
under orders to remove the pin at the word ‘‘ Ready,’’ and at the word ‘‘ Go”
the other mechanic who has assisted in starting the engine is under orders to
release the hook (H), and thus allow the car to dash down the track. In the
experiment on August 8 the mechanic failed to remove the pin (J) at the proper
time, and it was only after the machine had been released and started down
the track that it was seen that the pin had not been removed. It was then,
however, too late to stop it, so the car dashed down the track. Although the
striking of the board against the blocks caused the pin to split the board to
pieces, the launching apparatus worked perfectly and the aerodrome started off
on a perfectly even keel, the propellers revolving at an exceedingly high rate
of speed. The aerodrome flew straight ahead for a distance of 350 feet, when
it began to circle towards the right, descending slightly as it circled. Upon
completing a quarter cirele it again began to rise, flying straight ahead until
it had gone a similar distance, when it again lost headway, but before it reached
the water the engine increased its speed and the aerodrome again rose. When
the engine slowed down for the third time, however, the aerodrome was not many
feet above the river, so that before the engine regained its normal speed the
aerodrome touched the water with its propellers still revolving, but very slowly.
While the total distance covered was only about 1000 feet, and the time that it
was actually in the air 27 seconds, yet in this brief time it had served the main
purpose for which it had been built, which was to find out if the balancing of

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT " 259

the large aerodrome, which had been determined by calculation from the results
obtained with the steam-driven models, was correct. For it was assumed that
if the quarter-size model, which was an exact counterpart of the large machine,
should fly successfully with the same balancing as that caleulated for the large
one, the large one could reasonably be expected to act similarly. It was at first
thought best to make another test with the model immediately after recovering
it from the water, but by the time it could be brought into the house-boat and
the water which had got into the engine cylinders could be removed and the
engine made to work properly quite a strong wind had sprung up and rendered
further tests of the model on this day impossible. If the launching track for the
small machine could have remained on the top of the boat without interfering
with the completion of the preparations for testing the large machine, it would
have been left there and other tests made with the model when the weather was
suitable, but as this could not be done without interfering with the work on
the large machine, and the delays with the model had already been so great, the
small track was immediately removed and the model stored away in the house-
boat for possible later tests.

At the first it was impossible to account for the engine on the model run-
ning so irregularly and slowing down so soon after it was launched, as it was
felt very certain that the cylinders could not in so short a time, and with the
aerodrome actually moving through the air, have heated up sufficiently to cause
it. After a while, however, one of the workmen volunteered the information
that in his zeal to fill the fuel tank completely so as to insure a long flight,
he had caused the tank to overflow so that some of the gasoline had run into
the intake pipe, and that he had noticed gasoline dripping from the intake pipe
as the machine went down the track. This excess gasoline in the intake pipe
had caused the mixing valve which controls the quality of the explosive mix-
ture to be improperly set, so that it would not furnish the proper mixture when
the fuel was supplied in the proper way by the carburetor, and consequently
when this excess gasoline had evaporated, the mixture furnished to the engine
was not proper, and it consequently slowed down, there being no human intelli-
gence on board to correct the adjustment of the mixing valve.

A series of seven photographs of this flight of the quarter-size model is
given in Plates 87 to 93. Plate 87, taken with a kodak from the tug-boat sta-
tioned several hundred yards directly ahead of the house-boat, shows the ma-
chine in full flight heading directly for the tug-boat. Although the aerodrome
was about fifteen or twenty feet higher above the level of the water than the
camera, still, at the considerable distance from which the photograph was taken,
this view would not show so much of the under side unless the machine had
been pointing upward. The photograph also proves very clearly that at the
time it was taken the machine had certainly not dropped at all below the level

260 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

at which it was launched. In Plate 88 the camera was unfortunately not well
aimed, and only the front guy-post, bearing points, float and bowsprit are vis-
ible, besides the blur of the propellers, which, it will be noted, were moving
very rapidly. The camera with which this and the succeeding plates were taken
was one of the two special telephoto cameras belonging to the Zoological Park,
but built in the course of the aerodromic work and used where especially rapid
shutters were needed. As the shutters on these cameras give an exposure of
only 1/500 of a second, and consequently are sufficiently rapid to show the in-
dividual feathers in a rapidly moving bird’s wing, any distortion of the ma-
chine in flight would certainly have been shown, but, as will be seen from the
later photographs, no distortion of any kind occurred, both the surfaces and
the framework remaining in a perfectly straight condition. Near the bottom
of Plate 88 is the tug from which Plate 87 was taken, and a careful inspection
of Plate 87 shows two persons standing on the roof of the house-boat, below
the upper works, the gentleman on the left being Mr. Thomas W. Smillie, the
official photographer of the Smithsonian Institution, who took all of the photo-
graphs except Plate 87, and, as stated above, used therefor the special telephoto
cameras with the rapid shutters. Plate 89 is an exceedingly good view, and
shows the propellers revolving very rapidly while Plates 90, 91 and 92 show very
clearly that the speed of the propellers had greatly decreased between the suc-
cessive photographs. Plate 93 shows the aerodrome shortly after it touched
the water and had been almost completely submerged, in spite of its floats, by
the very strong tide which was running. Though these plates show all that
photographs can, they give no adequate idea of the wonder and beauty of the
machine when actually in flight. For while the graceful lines of the machine
make it very attractive to the eye even when stationary, yet when it is actually
in flight it seems veritably endowed with life and intelligence, and the spectacle
holds the observer awed and breathless until the flight is ended. It seems hardly
probable that anyone, no matter how skeptical beforehand, could witness a flight
of one of the models and note the almost bird-like intelligence with which the
automatic adjustments respond to varying conditions of the air without feeling
that, in order to traverse at will the great aerial highway man no longer needs
to wrest from nature some strange, mysterious secret, but only, by diligent
practice with machines of this very type, to acquire an expertness in the man-
agement of the aerodrome not different in kind from that acquired by every
expert bicyclist in the control of his bieyele.

In describing this flight immediately after it was made, Professor John M.
Manly, who took the photograph shown in Plate 87, said: ‘‘ The flight of the
small aerodrome was an event which all who saw it will remember for the
rest of their lives. We were, of course, in a state of considerable nervous ex-
citement and tension, for, after weeks of delay from high winds, rains, and

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 261

other uncontrollable causes, at last we had a day ideally suited to the test. This
was, to be sure, not the great test, the final test, the test of the man-earrying
flyer, but it was felt by all to be of almost equal importance, for if the bal-
ancing of the small aerodrome was correct, the large one would maintain its
equilibrium, and the problem of human flight would be solved practically as
well as theoretically. That the weather was now favorable for the test filled
us with excitement. Again and again the favorable moment had seemed to
come, and had gone again before we could make ready for it. The aero-
drome was rapidly carried to the upper works of the house-boat and the ob-
servers and helpers went hastily to their positions. The large tug-boat was sta-
tioned directly ahead, almost in the line of flight, and about a mile from the
house-boat. Signals of readiness were exchanged, and with every sense astrain
we awaited the supreme moment. The rocket gave the starting signal, and in-
stantly there rushed towards us, moving smoothly, without a quiver of its wings,
with no visible means of motion and no apparent effort, but with tremendous
speed, the strange new inhabitant of the air. Onward it moved, looking like a
huge white moth, but seeming no creature of this world, not only on account
of its size, its ease of movement and its wonderful speed, but also because of its
strange, uncanny beauty. It seemed visibly and gloriously alive as it advanced,
growing rapidly larger and more impressive. Straight at us it came, and for
a moment there was a wild fear that it would come right on and erush itself
against the ponderous tug-boat. There was a half impulse to move the tug-boat
out of its way, but the aerodrome seemed to realize its danger and rapidly,
though not abruptly or violently, as if it had intelligence and power of self-
direction, it checked its speed and circled to the right, descending slightly. Soon
it quickened its speed again and went straight ahead for about ten seconds,
when it again checked its flight and descended, circling once more. Once again
it attempted to increase its speed and rise, but it was too near the water, and
in a few moments the waves had wet its propellers and wings, and it sank, a
poor, bedraggled creature. But the vision of its beauty and power and seem-
ing intelligence and life will long remain with those who saw its flight.”
After removing the model-launching track so that the final arrangements
could be completed for testing the large machine, many weeks of delay were
experienced, almost entirely due to the unusually bad weather conditions which
prevailed, and which were unprecedented for the time of the year. However,
on September 3 the weather became more suitable, and the aerodrome being in
readiness the metal frame of the large machine was hoisted to the top of the
boat and placed on the launching car, and the wings, rudder, ete., were then
hoisted up and properly assembled and everything made ready for a flight.
The parties with the telephoto cameras were sent to their stations on the shore,

where definite base lines had been marked out so that with the data as to alti-
30

262 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

tude and azimuth, which these cameras automatically recorded, the speed, height,
ete., of the machine in flight could be accurately computed. After stationing
the tug-boats at proper points, so as to render assistance should the aerodrome
come down into the water at a considerable distance from the house-boat, it was
found, upon attempting to start the engine, that for some reason it would not
operate. The sparking battery which had been placed at the extreme rear of
the aerodrome was found to be giving such a weak spark that it would not
ignite the mixture in the cylinders. Upon removing the connection which
grounded the terminal of the battery to the framework and replacing it by a
large copper wire leading up to the engine so as to decrease the resistance of
the cireuit it was found that the battery still would not give sufficient spark.
A large quantity of dry cells, such as were used for the engine, had been pro-
cured to insure against delay from lack of batteries, but upon attempting to
get a new set from this reserve supply it was found that they, as well as the set
that was on the machine, had so deteriorated that instead of giving eighteen
amperes on short circuit they would give only three, which was not a sufficient
current to enable the engine to operate. No shop tests on the large engine had
been made since the large aerodrome had been brought down the river, as no
provision had been made for properly supporting the aerodrome in the house-
boat in such a way as to permit the large propellers to whirl around without caus-
ing damage, and, therefore, the batteries which had hitherto proved to be suitable
had not had any special test since they had been brought down the river. As no
batteries suitable for use were on hand, and as none could be procured from a
point nearer than Washington, the test had to be abandoned for the day and
the aerodrome removed to the interior of the boat.

It was at first impossible to account for the rapid deterioration of so large
a number of dry cells, but it was later found that the damp, penetrating fogs
which had been experienced for nearly two months were responsible for it, and
that in order to preserve the batteries in such a climate it was necessary to
place them in metallic boxes which could be nearly, if not quite, hermetically
sealed. New batteries were immediately procured from Washington, and before
again mounting the aerodrome on the launching track provision was made for
testing the engine inside the house-boat.

Up to this-time the wings had been stored inside the house-boat by sus-
pending them from the ceiling, but the time required to hoist them to the
upper works on top of the boat, after the main body of the aerodrome had
been placed on the launching car preparatory to making a flight, had added so
greatly to the delay, and consequently to the difficulty of getting the machine
entirely ready for a flight while the weather conditions remained suitable for
a test, that it was decided to build some framework on the upper works and
cover it with canvas so as to provide some boxes in which the wings could be

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 87

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903

merry

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

QUARTER-SIZE MCDEL AERODROME IN FLIGHT, AUGUST 8, 1903

VOL. 27, NO. 3, PL. 88

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 89

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL, 27, NO. 3, PL. 90

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 91

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 92

QUARTER-SIZE MODEL AERODROME IN FLIGHT, AUGUST 8, 1903

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 93

QUARTER-SIZE MODEL AERODROME AT END OF FLIGHT, AUGUST 8, 1903

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 94

HOISTING WING OF FULL-SIZE AERODROME 1

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 263

stored whenever it seemed probable that a flight would soon be possible. Some
of the difficulties experienced in hoisting these wings from the interior of the
boat to the upper works may be appreciated by an inspection of Plate 94, where
one of them is seen just ready to be hoisted from the raft. Only one wing at
a time could be handled on the raft, even when there was no appreciable wind
or roughness of the water, so that in order to hoist all four wings the raft had
to be hauled around from the door at the end of the boat to the side where the
wing was hoisted, and back again four times every time the machine was as-
sembled preparatory to a flight. The necessity for making occasional tests of
the engine in order to make sure that no trouble would be again experienced
in having proper batteries, etc., for the engine when the machine was again
on the point of being launched also made it imperative to remove the wings
from the interior of the house-boat, as the tremendous blasts of air from the
propellers would certainly have wrecked the wings had they remained in the
boat while the engine was being tested.

After the wings had been stored in the ‘‘ wing boxes,’’ thorough tests of
the engine were made, and before there came another day which was at all
suitable for a trial, it was accidentally discovered that the glued joints in the
cross-ribs of the large wings had been softened by the moisture of the fogs
which had penetrated everything, and that the joints had all opened up and
left the ribs in a practically useless condition.

It will be recalled from the description of these cross-ribs, Chapter VI, that
the rib is composed of two channel-shaped strips, the edges of which are glued
together while the strips are bent over a form which causes the ribs to main-
tain the curved form desired after the glue has hardened. Recalling these
facts, it will be readily understood that there is at all times a considerable strain
on the glued joints due to the two strips of wood trying to straighten out, and,
therefore, if the glue should at any time become softened sufficiently to allow
one strip to slide along on the other, the joint would open up and the rib would
consequently become straight. When the construction of the hollow ribs was
first contemplated it was realized that although the hollow construction would
enable the ribs to be strong, and at the same time exceedingly light, yet it
would make it imperative that the ribs be covered with a water-proof varnish
in order to prevent the glue from being softened when the aerodrome came down
into the water, as it was expected from the first that it would do at the end of
its flight. Considerable time and attention had, therefore, been given to this
very problem of securing a suitable water-proof varnish, and ribs coated with
the varnish which was finally used had been submerged in water for more than
24 hours in testing this very point, and no softening of the glue could be de-
tected after this long submergence. It had, therefore, been felt that the ribs
had been given a test which was much more severe than any conditions which

964 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

were likely to be met with, since the aerodrome would, in no ease which could
be anticipated, be in the water for so long a period as 24 hours, and no trouble
from this source need be anticipated.

In the present case, however, the moisture of the atmosphere, which had
been heavily laden with fog for several weeks, had penetrated the varnish and
softened the glue, even though the submergence of 24 hours in water had shown
no effect. To construct new ribs for the wings would have required several
weeks, and the delays which had already been experienced had by this time
prolonged the stay down the river so greatly that even under the very best
conditions it seemed hardly possible to complete the tests before the coming
of the equinoxial storms, which would make it necessary to remove the boat
from the middle of the river and place it in a safe harbor. Something, there-
fore, had to be done, and that very quickly, so that an immediate test could be
made, or else the tests would have to be delayed until the following season, or
possibly postponed indefinitely on account of the lack of funds.

Owing to the varnish with which the ribs were covered, it was impossible in
repairing them to carry out the first plan which suggested itself of binding the
ribs with a strip of cloth impregnated with glue and wound spirally from end
to end. As the wood was so very thin, it was impossible to bind the two parts
together with wire, and even thin bands of metal driven up on the tapered por-
tion of the rib were not likely to draw the two strips together without crush-
ing the wood. What was finally done was to scrape the edges of the two strips
where the joint had opened, thereby removing all the old glue, and after put-
tine fresh elue on all these edges the two strips were drawn together and bound
with surgeons’ tape, which was found to adhere very firmly even to the var-
nished surface.

After repairing the ribs in this manner and readjusting the guy-wires of
their framework so as to make the wing assume the correct form, which had
been slightly altered by the warping and twisting consequent on the opening up
of the ribs, everything was again in readiness for a test in free flight, numer-
ous tests of the engine having meanwhile been made both with the aerodrome
frame inside of the house-boat and also when mounted on the launching track
above. The weather, which had been unprecedentedly bad all summer, now be-
came even worse, and although short periods of calm lasting an hour or less
occasionally oceurred, there were for several weeks no calm periods long enough
for completing the necessary preparations and making a test, although the time
required for assembling the aerodrome had been greatly shortened by building
the ‘‘ wing boxes’? on the superstructure, and in other ways previously de-
scribed. On several occasions when an attempt was made to utilize what ap-
peared to be a relative calm, the aerodrome was assembled on the launching
apparatus and everything got in readiness except the actual fastening of the

NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 265
wings and rudder to it, but in every instance, before the wings could be actually
applied and a flight made, the wind became so strong as to absolutely prohibit
a test. On two occasions when the wings were actually attached, heavy rain
storms suddenly came up and drenched the machine before the wings could be
removed, and on several occasions it was necessary to leave the entire metal
frame and engine of the aerodrome mounted on top of the boat al! night, be-
cause the heavy sea which was running made it impossible to utilize the large
raft in returning the frame to the interior of the boat.

Finally, however, after it seemed almost useless to hope for calm weather,
what appeared to be a most propitious day arrived on October 7. The wind
which had been quite high in the early morning gradually quieted until at 10
a.m. it was blowing only about twelve miles per hour and the indications were
that it would quiet down still more. Every energy was concentrated in getting
the aerodrome ready at the earliest possible moment, as previous experience
had shown too clearly that the conditions might be completely reversed in less
than an hour. As the tide and wind caused the boat to swing up the river from
its buoy, and thus made the launching track point down the river, the steam
tug-boat was sent down the river for a distance of a mile or more so that,
should the aerodrome come down into the water without being able to make a
return trip to the house-boat, the tug-boat would be able to reach it quickly
and render assistance to both the writer and the machine should they need it.
At 12.20 p.m. everything was in readiness and what appeared to be the decisive
moment had arrived, when the writer, after starting up the engime and grad-
ually raising its speed to the maximum, and after taking the last survey of the
whole machine to insure that everything was as it should be, finally gave the
orders to release it.

Although the writer did not have the privilege of seeing it glide down the
track, as his attention was too thoroughly engaged in insuring that he was in
the proper position for reaching immediately any of the control apparatus,
either of the aerodrome or of the engine, yet those who did witness the actual
passage of the machine down the track have said that the sight was most im-
pressive and majestic. No sign of jar was apparent when the machine was
first released, but with lightning-like rapidity it gathered its speed as it rushed
down the sixty feet of track, the end of which it reached in three seconds, at
which time it had attained a speed of something over thirty-two feet per sec-
ond. Just as the machine reached the end of the track the writer felt a sud-
den shock, immediately followed by an indescribable sensation of being free in
the air, which had hardly been realized before the important fact was intui-
tively felt that the machine was plunging downward at a very sharp angle, and
he instinctively grasped the wheel which controls the Pénaud tail and threw
it to its uppermost extent in an attempt to depress the rear of the machine and

266 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

thereby overcome the sharp angle of descent. Finding that the machine made
no response to this extreme movement of the tail, he immediately realized that
a erash into the water was unavoidable and braced himself for the shock. The
tremendous erash of the front wings being completely demolished as they struck
the water had hardly become apparent before he found himself and the machine
plunging downward through the water. By some instinct he grasped the main
euy-wires which were above his head, and pulling himself through the narrow
space between them freed himself from the machine and swam upward as rap-
idly as possible. A few moments after reaching the surface of the water the
uppermost point of the pyramid of the machine was seen to project from the
water and he swam over and sat down on it until a row-boat could be sent to
it from the nearby power-boat.

The first thing that the writer saw after looking around him was a news-
paper reporter, his boatman expending the utmost limit of his power in push-
ing his boat ahead to be the first one to arrive.

After giving directions to the workmen regarding the recovery of the ma-
chine, the writer returned to the house-boat to obtain dry clothing, and although
his first inclination was not to make any statement until a complete examina-
tion could be made to determine both the cause of the lack of success and also
the extent of the damage which had been sustained by the machine, yet owing
to the very great pressure brought to bear by the press representatives who
said that unless some statement was given out they would write their own
conclusions as to the cause of the mishap, he finally gave out the following

statement :
STATEMENT MADE BY MR. MANLY TO ASSOCIATED PRESS

‘¢ Tt must be understood that the test to-day was entirely an experiment, and
the first of its kind ever made. The experiment was unsuccessful. The bal-
ancing, upon which depends the success of a flight, was based upon the tests
of the models and proved to be incorrect, but only an actual trial of the full-
size machine itself could determine this. My confidence in the future success of
the work is unchanged. I can give you no further information. I shall make a
formal report to Secretary Langley.’’

After recovering the machine the foreman of the workmen (Mr. Reedy
[who together with Mr. McDonald were the only ones on top of the boat when
the launching actually took place], busied himself to discover what had caused
the jerk to the machine at the moment it was released, which had been imme-
diately followed by the great depression of the front end. After some little
time he discovered that the upright guide at the extreme front of the launch-
ing car (which, as heretofore stated, was slotted to receive a metal lug project-
ing from the end of the guy-post, and thus prevent the front end of the frame-

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO, 3, PL. 95

FLIGHT OF LARGE AERODROME, OCTOBER 7, 1903

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No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 267

work from being twisted by a side wind striking the machine while it was still
on the launching car) had been distorted, the metal cap on it being stretched
out of shape in a way which indicated that the pin of the front guy-post had
hung in the cap, and that the guy-post was not therefore free from this part
of the car when the end of the launching track dropped. The shock which the
writer felt at the moment of launching and which had also been seen by others
to occur was thus conclusively shown to have been due to the falling track,
dragging the front end of the machine down with it. As the machine was trav-
elling forward and the car had been almost instantly brought to a standstill by
its buffer pistons co-acting with the buffer cylinders at the foot of the track,
this front guy-post had been pulled backwards, and thus not only pulled the
main guy-wires of the wings backwards and thereby depressed the front edge
of the front wings so that they had no angle of inclination, but had also bent
the front end of the metal framework downward,—effects which were dis-
covered from the later examination of the frame and the guy-post itself. From
the instantaneous photographs which were obtained, indisputable evidence was
obtained that this was what actually oceurred. Referring to the photograph,
Plate 95, which was taken by Mr. G. H. Powell, Secretary of the Board of Ord-
nance and Fortification, and which shows the machine just a few feet in front
of the point where it was actually launched, it will at once be seen that the
front end of the frame is bent downward and that the front guy-post instead of
being parallel with the rear one has been deflected backward at the lower end
through an angle of 30 degrees. Referring further to the photograph, Plate
96, which was taken at the same instant as the one just described, it will be
seen that even this one, which is a view of the machine as it passed almost
directly over Mr. Smillie’s head, most clearly shows the extreme extent to which
the front wings had been distorted, the rear edges of the wings near the frame
having been twisted up until they struck the cross-frame, and the outer ends
being free to twist had been forced up very much higher.

After completing the recovery of the machine and the examination as to
the extent of the injuries it had sustained, and finding unquestionable evidence
that the accident had been caused by the front guy-post hanging in its guide
block on the launching car, the workmen were set to work straightening out and
arranging the various parts, fittings and accessories, and cleaning up the en-
gine which fortunately had sustained no injury whatever. After a consulta-
tion in Washington with Mr. Langley, who had been unable to be present at
the experiment, both concerning what had already occurred and also what should
be done regarding the future of the work, and in view of the fact that the
statement which the writer had given to the press representatives, immediately
after the accident, had been made before there had been time to make an examina-
tion of the machine itseif, it was decided that it would be best to give to the press

268 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

a short statement to correct the earlier one, and Mr. Langley accordingly made
public the following note:

‘‘ Mr, Langley states that he was not an eye witness of the experiment at
Widewater yesterday, having been detained in Washington by business, but that
on the report of Mr. Manly, immediately in charge, he is able to say that the
latter’s first impression that there had been defective balancing was corrected
by a minuter examination, when the elutch, which held the aerodrome on the
launching ways and which should have released it at the instant of the fall, was
found to be injured.

‘© The machinery was working perfectly and giving every reason to antici-
pate a successful flight, when this accident (due wholly to the launching mech-
anism) drew the aerodrome abruptly downward at the moment of release and
cast it into the water near the house-boat. The statement that the machine failed
for lack of power to fly was wholly a mistaken one.

‘The engine, the frame and all the more important parts were practically
uninjured. The engine is actually in good working order. The damage done was
confined to the slighter portions, like the canvas wings and propellers, and these
ean be readily replaced.

‘¢ The belief of those charged with the experiment in the ultimate success-
ful working of the machine is in no way affected by this accident, which is one
of the large chapter of accidents that beset the initial stages of experiments so
novel as the present ones. It is chiefly unfortunate in coming at the end of the
season when outdoor work of this sort is impossible.

‘¢ Whether the experiments will be continued this year or not has not yet
been determined.’’

In view of the many inaceurate accounts published in the daily press at
the time of this experiment, special attention is directed to the fact that even
under the enormous strain to which the aerodrome was subjected, due to its
striking the water at an angle of approximately forty-five degrees and at a
speed certainly not less than forty miles an hour, no bending or distortion of
any kind was found in the frame after it was recovered, except that a slight
depression at the front had been produced by the lower guy-post catching on
the launching car, as previously described. This is very clearly seen in Plate
97, Fig. 1, which shows the aerodrome being hoisted from the water, and in
Plate 97, Fig. 2, which shows it just afterwards resting on the raft, the wings,
tail and rudder having been completely demolished by towing it through the
water to the house-boat from the place where it struck the water. This single
distortion, therefore, was in no way a result of the strains experienced by the
frame either while it was in the air or when it struck the water. Some of the
press reports, and, in fact, some of the accounts published in the scientific press,
stated that the aerodrome frame had proved so weak that it broke while the
machine was in the air, and that this was the cause of the accident. Nothing
could be farther from the actual facts than this, for though there were many
things connected with the machine which could not be properly tested until it
was actually in the air, yet the strength of the frame had been most thoroughly

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 269

tested in the shops prior to the trial, and it had been found that with the frame
supported only at the extreme front and rear, no appreciable deflection was
produced upon it by the concentrated weight of four men at the center, even
when they simultaneously jumped up and down on it. That the aerodrome
frame was amply strong was further evidenced by the fact that in the later
trial, hereafter described, no injury was sustained by the frame even when the
machine turned over in mid-air and struck the water flat on its back. In fact,
no point regarding the aerodrome is more certain than that the frame was more
than strong enough for its purpose.

Plates 98 to 100 show the aerodrome in the water from the moment after it
arose and the writer, who had extricated himself while it was plunging down
through the water and beat it to the surface, had swum over to it and sat down
on the upper pyramid to await a row-boat, until the machine was taken in tow
by the tug-boat.

As the weather conditions were continually growing worse, owing to the
lateness of the season, it was decided that it would be absolutely impossible to
undertake to keep the house-boat down the river until the aerodrome could be
repaired and another test made, and the writer accordingly returned to Quan-
tico on the following day, expecting to take the tug-boat from there to the
house-boat and complete arrangements for bringing everything to Washington.
On reaching Quantico, however, it was found that a most violent storm was
raging on the river, and had, in fact, been increasing in violence since the even-
ing of October 7, immediately following the trial. On account of the storm it
was impossible to reach the house-boat or to get into communication with the
workmen, who had sought refuge at the hotel at Clifton Beach, as the tug-boat
itself was not at the point at which it was expected to be found, and, in fact,
it had not been seen by any of the river people since the morning of October 8,
when it was seen taking the workmen from the boat to Clifton Beach. Two days
later, or October 11, when the storm had subsided and the tug-boat, which had
been blown many miles down the river, was able to return the workmen to the
house-boat, it was found that the storm had made a complete wreck of all the
row-boats, the power-launch, and the large raft. The row-boats had been com-
pletely demolished on the beaches, the launch had been broken from its moor-
ings to the house-boat and driven ashore some four miles down the river, where
it was found with the deck torn completely off, a large hole stove in it amid-
ships, and the engine seriously damaged, while the raft had been very seriously
damaged on the beach many miles down the river. After making temporary
repairs to the raft and getting it launched, it was used as a floating dock for
making temporary repairs on the power-launch; both were then returned to
their moorings at the house-boat and everything got in readiness for towing
the house-boat to Washington, and this was finally accomplished on October 12.

31

270 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

Even while the boat was en route some of the workmen were busily engaged in
the repair of the damaged parts, the others having been sent ahead to Wash-
ington to begin work on the construction of new wings, so that another trial
could be had at the earliest moment that the weather would permit.

One extra pair of wings was on hand, but these had been stored in the
house-boat while it was down the river, and the damp weather, which had caused
such serious damage to the cross-ribs of the wings which were actually used,
had also so seriously affected the ribs of these extra wings that it was neces-
sary to diseard some of them and repair the others. An extra Pénaud tail was
on hand, as well as a steering rudder, and it was estimated that unless some
unforeseen delay occurred the aerodrome would be ready for flight in three
weeks.

After making a careful examination of the places on the river which seemed
most available for an experiment, it was finally decided to make the next test
just off the Potomac Flats, at the junction of the main body of the river and
the Eastern Branch, the traffic on this part of the river, which would have been
more dangerous and troublesome during the summer, being quite light at this
time of the year. By making the experiment at this point it was possible to
leave the house-boat at its dock until the weather seemed suitable and then have
a tug-boat tow it to the exact point, which would be determined by the state of
the wind and the tide.

After more completely examining the condition of the framework of the
machine, and discussing and maturely deliberating on the causes which had led
to the accident of October 7, the writer advised Mr. Langley not to make any
changes either in the machine itself or in the launching apparatus, except to
remove the small lug from the metal rod which projected from the end of the
guy-post, and which by catching in its guide on the launching car had been the
sole cause of the accident. The aerodrome was accordingly repaired so as to
reproduce exactly the conditions which obtained at the time of the previous ex-
periment, except for this slight change, and it was again ready for trial by
the middle of November. The weather, however, at this time was very vari
able, there being at times comparatively quiet periods which lasted for only an
hour or less, which was not sufficient time for procuring a tug-boat and towing
the boat to the proper point, and then assembling the aerodrome and making a
trial. However, after many days waiting, what appeared to be an exception-
ally quiet day oceurred on December 8, the wind quieting down by noon to such
an extent that practically a dead calm prevailed. Vigorous search was imme-
diately instituted for a tug-boat to tow the house-boat to the point selected,
but it was very late in the afternoon before one could be procured, and by the

time the boat arrived at the proper place darkness was descending and a strong

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 97

AERODROME BEING RECOVERED, OCTOBER 7, 1903

.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 98

AERODROME IN WATER, OCTOBER 7, 1903

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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 99

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AERODROME IN WATER, OCTOBER 7, 1903

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

VOL. 27, NO. 3, PL. 100

AERODROME IN WATER, OCTOBER 7, 1903

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NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 271

and exceedingly gusty wind had sprung up, and it seemed almost disastrous
to attempt an experiment.

However, the funds which had been appropriated by the Board of Ord-
nance and Fortification had been exhausted nearly two years before, and all the
expense since that time had been met from a special fund of the Smithsonian
Institution. But, owing to the heavy drains which the work had made upon
this fund, Mr. Langley felt unwilling to draw further upon it, and since there
were no other funds available from which to meet the expenses which would
be incurred by postponing the experiments until spring, it was decided that it
was practically a case of ‘‘ now or never,’’ and although the river was full of
large blocks of floating ice several inches thick, which added enormously to the
danger involved in the experiment, the writer decided to make the test imme-
diately so that the long-hoped-for success, which seemed so certam, could be
finally achieved.

After considerable delay, due to the great difficulty of properly assembling
the huge wings in the strong and gusty wind, into which the beat could not be
kept directly pointed, owing both to the strong tide which was running and to
the fact that the wind itself was rapidly varying through as great a range as
ninety degrees, and after many minor delays, due to causes too numerous to
mention, the aerodrome was finally ready for test.

The wind was exceedingly gusty, varying in velocity from twelve to eight-
een miles per hour and shifting its direction most abruptly and disconcert-
ingly, so that the aerodrome was at one moment poimted directly into it and at
the next moment side gusts striking under the port or starboard wings would
wrench the frame severely, thus tending to twist the whole machine from its
fastenings on the launching car. After starting up the engine and bringing
it to full speed, the writer gave the signal for the machine to be released, and
it started quietly, but at a rapidly accelerated pace, down the launching track.
Exactly what happened, either just before or just as the aerodrome reached
the end of the track, it has been impossible to determine, as all the workmen
and visitors had gone to their stations on the various auxiliary boats, except
the two workmen (Mr. Reed and Mr. McDonald) who had been retained on
top of the boat to assist in the launching. It had grown so dark that the cam-
eras of Mr. Smillie, the official photographer, were unable to get any impres-
sion when he used them, owing to the extreme rapidity of the shutters with
which they were equipped. Fortunately, one photograph of the machine while
still in the air was secured, which shows the result of what had occurred in the
launching and before any further damage had been caused by its coming down
into the water, but the all-important question as to just what caused the acci-

dent which did occur remains to a certain extent a mystery.

PAB SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VoL. 27

Mr. Reed, the foreman, who was qualified to observe accurately, not only
through his having worked continuously for many years on the machines, but
also from his having witnessed the numerous tests of the models, states that
from his position near the rear end of the launching track he noticed that at a
point about ten feet before the machine reached the end of the track the Pénaud
tail seemed to have dropped at the rear end in some inexplicable way so that
it was dragging against the cross-pieces of the track, and that at the next in-
stant, when the ear reached the end of the track, he saw the machine continue
onward, but the rudder and whole rear portion of the frame and the wings
seemed to be dragging on the launching ear. Mr. McDonald, the head machin-
ist, states that he had his attention so concentrated on the engine, which he
noticed was working perfectly and driving the propellers at a higher rate of
speed than he had ever before seen it do, that he did not see anything happen
until he saw the machine shoot upward in the air, gradually attaining a verti-
cal position with its bow upward, where it was sustained for a few moments by
the upward thrust of the propellers. After a few moments, however, the strong
wind, which was blowing from twelve to eighteen miles an hour directly ahead
and acting against the wings which were now vertical, drove the machine back-
wards towards the house-boat, and he saw it come down into the water on its
back, with the writer gradually righting himself in accordance with the turn-
ing of the machine until he was finally hidden from view by the machine com-
ing down on top of him. The witnesses on the tug-boats seem not to have been
able to perceive exactly what occurred. <All unite in stating that something
seemed to happen to the machine just a few feet before the launching car
reached the end of the track, but what it was they could not say. Everyone
who saw the accident and who was sufficiently familiar with the construction of
the machine to be able intuitively to form an idea as to just what was taking
place was so very close to the machine that when the accident happened every-
thing seemed to merge into one vision, which was that of the whole rear of
the wings and rudder being completely destroyed as the machine shot upward
at a rapidly increasing angle until it reached the vertical position previously
mentioned.

The writer can only say that from his position in the front end of the ma-
chine, where he was facing forward and where his main attention was directed
towards insuring that the engine was performing at its best, he was unable to
see anything that occurred at the rear of the machine, but that just before the
machine was freed from the launching car he felt an extreme swaying motion
immediately followed by a tremendous jerk which caused the machine to quiver
all over, and almost instantly he found the machine dashing ahead with its bow
rising at a very rapid rate, and that he, therefore, swung the wheel which con-
trols the Pénaud tail to its extreme downward limit of motion. Finding that

ee ee

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 273

this had absolutely no effect, and that by this time the machine had passed its
vertical position and was beginning to fall backwards, he swung himself around |
on his arms, from which he supported himself, so that in striking the water with
the machine on top of him he would strike feet foremost. The next few mo-
ments were for him most intense, for he found himself under the water with the
machine on top of him, and with his cork-lined canvas jacket so caught in the fit-
tings of the framework that he could not dive downward, while the floor of the
aviator’s car, which was pressing against his head, prevented him from coming
upward. His one thought was that if he was to get out alive he would have
to do so immediately, as the pressure of the water on his lungs was beginning
to make itself seriously felt. Exerting all of the strength he could muster, he
succeeded in ripping the jacket entirely in two and thus freeing himself from
the fastenings which had accidentally held him, he dived under the machine and
swam under the water for some distance until he thought he was out from un-
der the machine. Upon rising to the surface his head came in contact with a
block of ice, which necessitated another dive to get free of the ice. Upon com-
ing to the surface of the water he noticed Mr. Hewitt, one of the workmen, just
about to plunge in; before he could call out to indicate he was safe, Mr. Hewitt
had heroically plunged in with the expectation of diving under the machine
where he believed the writer to be entangled. Finding the house-boat was be-
ing rapidiy shoved upon him, imperilling the life of both himself and Mr. Hewitt,
besides the safety of the aerodrome, the writer gave orders that the tug-boat
reverse and tow the house-boat away. Then, with the assistance of a row-boat,
he reached the house-boat, where willing hands drew him on board and assisted
him into dryer and warmer clothing. :

Meanwhile, it had become quite dark, and when the writer went outside to
see about the aerodrome he found that the men on the tug-boat, in their zeal to
render assistance, had fastened a rope to the rear end of the machine, at the
same time pulling it in the direction in which the front end was pointed, and
through their ignorance had forced it down into the muddy bottom of the river
and broken the main framework completely in two, thus rendering it absolutely
impossible with the facilities at hand to remove it from the water to the in-
terior of the boat. It was finally necessary to tie the wrecked machine to the
stern of the house-boat and have the boat towed to its dock where the mast and
boom were assembled and the wrecked machine hoisted from the water. This
was finally accomplished about midnight, when the workmen, who had been work-
ing at a fever heat all day, were glad to close up the work for the day, which
had proved so unfortunate.

As has already been remarked, darkness had descended to such an extent
that the light was not strong enough to give photographs with the very rapid

shutters with which Mr. Smillie had his cameras equipped, and that, therefore,
32

274 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

incontrovertible evidence, which the instantaneous photographs had given as to
just what had occurred to the machine in the accident of October 7, was in this
case unfortunately lacking. It was at first thought that no photographs had
been obtained while the machine was actually in the air, but it was later found
that by some rare fortune the photographer for The Washington Star had se-
eured a photograph, which, while small, showed very distinctly some decidedly
interesting facts. An enlargement of this photograph is shown in Plate 101, by
the kind permission of The Washington Star. Referring to this photograph,
it will be seen that at the moment it was taken the machine was practically ver-
tical in the air, and it confirms the testimony of the eye witnesses, and also the
writer’s impression that the machine was maintained in a vertical position for
several moments by the upward thrust of the propellers. It will also be seen
that the Pénaud tail has been completely demolished and is hanging as a limp
roll of cloth, which the strong wind has deflected backwards towards the house-
boat, the port rear wing has broken its main ribs, both where they are attached
to the main frame and also about midway the length of the wing, the outer end
being partially folded towards the frame. The starboard rear wing has also
broken both of its main ribs at the point where they are joined to the frame,
and they have also broken at a point about one-third their length from the frame,
the outer end being likewise folded towards the frame. By a still more careful
inspection, it will also be seen that the port front wing is apparently uninjured,
while the starboard front wing has broken the’ middle main rib at a point be-
tween the sixth and seventh cross-ribs, and while it cannot be distinctly seen at
first that the front main rib has also broken at the same point very careful in-
spection will show that this is the case, as the sixth and seventh ribs, showing
as faintly darker lines in the photograph, are seen to be displaced, so that they
are together and actually crossing each other. It will furthermore be seen that
both front wings have been pressed upward by the wind until their tips near
the inner ends are in contact with the cross-frame. This could not have hap-
pened unless the front guy-post had given away either by bending or breaking.
The fact that it has given way is further evidenced by a more careful examina-
tion of the extreme front end of the machine, where it will be seen that the bow-
sprit and the curved tubes which form the extreme end of the steel frame have
been bent from a straight line with reference to the main frame. This bend-
ing of the bowsprit and the curved tubes could be produced only by the front
guy-post coming in contact with some obstruction on the launching car as the
machine left it. It is known very certainly that the rear end of the machine
came in contact with the launching ear, as the car itself shows a very deep gash
in the wooden cross-piece at its center, which was produced by the port-bear-
ing point at the rear striking it. As this bearing point was elevated five feet
above the cross-piece of the launching car, and was also six feet six inches to

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27, NO. 3, PL. 101

a

ATTEMPTED LAUNCHING OF AERODROME, DECEMBER 8, 1903

ENLARGEMENT OF PHOTOGRAPH BY THE WASHINGTON STAR

‘J ton

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 275

the rear of the point where the wood is torn, this rear-bearing point must

have travelled downward at an angle of approximately thirty-eight degrees in

order for the bearing point to strike the car at this point. As the lower end of

the rear guy-post was only eighteen inches above the cross-piece of the launch-

ing car, it, of course, would be broken before the bearing point could descend

so much. As has been previously stated, Mr. Reed, who was at the rear of the

launching track, states very positively that the rudder was dragging on the

track at least ten feet before the launching car reached the front end of the

track where the machine was actually launched. There are several ways in

which the rudder could have gotten down on the track, but positive informa-

tion is lacking. If it was dragging on the track, as Mr. Reed states (and from

his extended experience and rather acute powers of observation I should place

great credence in his report), the subsequent demolition of the guy-posts sue-

ceeded by the destruction of the rear wings and serious injury of the front

ones is easily explained. If the dropping of the rudder on the track occurred

from the breaking of the upper rudder post, over which the upper control wire

passed, the lower vertical surface would first come in contact with the track,

and the destruction of this part would certainly occasion subsequent destruc-
tion of the horizontal and upper vertical surfaces of the rudder, leaving the

central rib of the rudder still attached to the frame, and upon the machine be-

ing released from the car a few moments later this destroyed rudder would

easily catch in the launching car and pull the aerodrome down on it, and thus

cause the destruction of the guy-posts, wings, and so forth. If the dropping of

the rudder was caused primarily by its main rib breaking loose from its con-
nection with the frame, the rudder would still be dragged along behind the ma-
chine by the wire cords through which it was operated, and the subsequent
launching of the machine would still give the rudder every chance to catch in
the launching car and drag the machine down on it.

It can therefore be said that, while positive information is lacking, there is
very strong evidence that the accident in the launching was due to the rudder
becoming entangled with the launching track owing to the breakage of some
part of the mechanism by which it was connected to the main frame.

It is of importance to note that the photograph furnishes incontrovertible
evidence that the main frame of the machine was in no way injured, except for
the slight bending of the forward curved extension, and that, therefore, the ac-
cident was in no way due to the weakness of the frame. The main frame was
not even injured by the machine coming down in the water on its back, and the
later damage was entirely caused by the combination of the ignorance of the
tug-boatmen and the darkness in which they were working, when they attempted
to tow it to the rear of the house-boat so that it could be removed from the water.

276 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

On the day following the trial a very careful inspection was made in the
hope of obtaining some more definite information as to just what caused the
accident, but the serious injury to the machine caused by the tug-boatmen break-
ing it in the water had so greatly tangled things up that it was impossible to
tell anything about it. The workmen were immediately put to work removing
fittings from the broken wings, rudder, ete., and dismounting the engine, which
was immediately reassembled on its testing frame and found to be absolutely
uninjured. The transverse frame of the machine was comparatively uninjured,
the damage done by the men on the tug-boat being the breaking of the machine
in two at a point just back of the cross-frame, together with the consequent de-
struction of the bearing points, ‘‘ trestle,’’ and certain fittings by which the
main guy-wires were attached to the main tubes and the pyramids.

The situation which now existed was most distressing and disheartening.
Mr. Langley felt that he could not approve of further expenditures from any
Smithsonian fund, and the Board of Ordnance and Fortification of the War De-
partment having been severely criticised on the floors of Congress for its orig-
inal allotment for the work, deemed it inexpedient to incur a possible curtail-
ment of the funds annually placed at its disposal for general experimental
work through a manifestation of continued interest in the flying machine.

As has already been stated, representatives from the Board of Ordnance
and Fortification of the War Department were present at both tests of the
large aerodrome; on October 7 Major Montgomery M. Macomb and Mr. G. H.
Powell, and on December 7 General W. IF’. Randolph accompanied by Major
Macomb and Mr. Powell, represented the War Department, and Dr. K. 8. Nash,
at that time Contract Surgeon, U. 8. A., was officially present at both trials to
render medical assistance should it be needed.

By permission of the War Department, the official report of the tests sub-
mitted by Major Macomb to the Board of Ordnance and Fortification is here
made public:

Ene.-1st to 3d end’t, BOF 6191.

ReEpPortT

Experiments with working models which were concluded August 8 last hav-
ing proved the principles and calculations on which the design of the Langley
aerodrome was based to be correct, the next step was to apply these principles
to the construction of a machine of sufficient size and power to permit the carry-~
ing of a man, who could control the motive power and guide its flight, thus point-
ing the way to attaining the final goal of producing a machine capable of such
extensive and precise aerial flight, under normal atmospheric conditions, as to
prove of military or commercial utility.

Mr. C. M. Manly, working under Prof. Langley, had, by the summer of 1903,
succeeded in completing an engine-driven machine which under favorable atmos-

rth

a

No. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 277

pheric conditions was expected to carry a man for any time up to half an hour,
and to be capable of having its flight directed and controlled by him.

The supporting surface of the wings was ample, and experiment showed the
engine capable of supplying more than the necessary motive power.

Owing to the necessity of lightness, the weight of the various elements had
to be kept at a minimum, and the factor of safety in construction was therefore
exceedingly small, so that the machine as a whole was delicate and frail and in-
capable of sustaining any unusual strain. This defect was to be corrected in
later models by utilizing data gathered in future experiments under varied
conditions.

One of the most remarkable results attained was the production of a gas-
oline engine furnishing over fifty continuous horse-power for a weight of one
hundred and twenty pounds.

The aerodrome, as completed and prepared for test, is briefly described ie
Prof. Langley as ‘‘ built of steel, weighing complete about seven hundred and
thirty pounds, supported by one thousand and forty feet of sustaining surface,
having two propellers driven by a gas engine developing continuously over fifty:
brake horse-power.’’

The appearance of the machine prepared for flight was exceedingly light
and graceful, giving an impression to all observers of being capable of success-
ful flight.

On October 7 last everything was in readiness, and I witnessed the at-
tempted trial on that day at Widewater, Va., on the Potomac. The engine
worked well and the machine was launched at about 12.15 p.m. The trial was
unsuccessful because the front guy-post caught in its support on the launching
car and was not released in time to give free flight, as was intended, but on the
contrary, caused the front of the machine to be dragged downward, bending
the guy-post and making the machine plunge into the water about 50 yards in
front of the house-boat. The machine was subsequently recovered and brought
back to the house-boat. The engine was uninjured and the frame only slightly
damaged, but the four wings and rudder were practically destroyed by the first
plunge and subsequent towing back to the house-boat. This accident necessi-
tated the removal of the house-boat to Washington for the more convenient re-
pair of damages.

On December 8 8 last, between 4 and 5 p.m., another attempt at a trial
made, this time at the junction of the Anacostia with the Potomac, just eee
Washington Barracks.

On this occasion General Randolph and myself represented the Board of
Ordnance and Fortification. The launching car was released at 4.45 p.m., be-
ing pointed up the Anacostia towards the Navy Yard. My position was on the
tug Bartholdi about 150 feet from and at right angles to the direction of pro-
posed flight. The car was set in motion and the propellers revolved rapidly,
the engine working perfectly, but there was something wrong with the launch-
ing. The rear guy-post seemed to drag, bringing the rudder down on the launch-
ing ways, and a crashing, rending sound, followed by the collapse of the rear
wings, showed that the machine had been wrecked in the launching, just how, it
was impossible for me to see. The fact remains that the rear wings and rudder
were wrecked before the machine was free of the ways. Their collapse deprived
the machine of its support in the rear, and it consequently reared up in front
under the action of the motor, assumed a vertical position, and then toppled
over to the rear, falling into the water a few feet in front of the boat.

bo

78 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

Mr. Manly was pulled out of the wreck uninjured and the wrecked machine
was subsequently placed upon the house-boat, and the whole brought back to
Washington.

From what has been said it will be seen that these unfortunate accidents
have prevented any test of the apparatus in free flight, and the claim that an
engine-driven, man-carrying aerodrome has been constructed lacks the proof
which actual flight alone can give.

Having reached the present stage of advancement in its development, it
would seem highly desirable, before laying down the investigation, to obtain
conclusive proof of the possibility of free flight, not only because there are ex-
cellent reasons to hope for success, but because it marks the end of a definite
step toward the attainment of the final goal.

Just what further procedure is necessary to secure successful flight with
the large aerodrome has not yet been decided upon. Professor Langley is un-
derstood to have this subject under advisement, and will doubtless inform the
Board of his final conclusions as soon as practicable.

In the meantime, to avoid any possible misunderstanding, it should be stated
that even after a successful test of the present great aerodrome, designed to
carry a man, we are still far from the ultimate goal, and it would seem as if
years of constant work and study by experts, together with the expenditure of
thousands of dollars, would still be necessary before we can hope to produce an
apparatus of practical utility on these lines.

M. M. Macoms,
WasuHincron, January 6, 1904. Major Artillery Corps.

The attitude of the Board of Ordnance and Fortification, with reference to
rendering further financial assistance to the work, is clearly shown by the fol-
lowing extract from the official report of the Board on October 6, 1904, to the
Secretary of War:

THE LANGLEY AERODROME

Early in the year 1898 a board composed of officers of the Army and Navy
was appointed to examine the models and principles of the aerodrome devised
by Dr. S. P. Langley, Secretary of the Smithsonian Institution, and to report
whether or not, in its opinion, a large machine of this design could be built, and,
if so, whether it would be of practical value.

The report of this board was referred to the Board of Ordnance and For-
tification for action, and Doctor Langley was invited to appear before the Board
and further explain the proposed construction.

In view of the great utility of such a device, if a practical success, the
Board, on November 9, 1898, made an allotment of $25,000 for the construction,
development, and test of an aerodrome to be made under the direction of Doctor
Langley, with the understanding that an additional allotment of the same amount
would be made later. On December 18, 1899, the additional allotment of $25,-
000 was made.

The construction of the machine was delayed by Doctor Langley’s inabil-
ity to procure a suitable motor, which he was finally obliged to design. The
aerodrome was completed about July 15, 1903, and preparations for its test
were made at a point in the Potomac River about 40 miles below Washington.

fT =

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 279

Preliminary arrangements having been completed and tests made of a quarter-
size model, the first attempt at actual flight with the man-carrying aerodrome
was made on October 7, 1903.

On this occasion there were present on behalf of the Board, Major M. M.
Macomb, Artillery Corps, and Mr. G. H. Powell, clerk of the Board.

Major Macomb in his report to the Board stated that—

‘* The trial was unsuccessful because the front guy-post caught in its support
on the launching car and was not released in time to give free flight, as was in-
tended, but on the contrary, caused the front of the machine to be dragged down-
ward, bending the guy-post and making the machine plunge into the water
about 50 yards in front of the house-boat.’’

This accident necessitated the removal of the house-boat to Washington for
the more convenient repair of damages. The repairs having been completed,
on December 8, 1903, another attempt at a trial was made, this time at the
Junction of the Anacostia and the Potomac Rivers. General W. F. Randolph
and Major Macomb, members of the Board, and Mr. Powell, were present.
Major Macomb reported as follows:

‘« The launching car was released at 4.45 p. m. ... The car was set in motion
and the propellers revolved rapidly, the engine working perfectly, but there was
something wrong with the launching. The rear guy-post seemed to drag, bring-
ing the rudder down on the launching ways, and a crashing, rending sound, fol-
lowed by the collapse of the rear wings, showed that the machine had been
wrecked in the launching, just how, it was impossible for me to see.’’

March 3, 1904, the Board stated that it was not ‘‘ prepared to make an
additional allotment at this time for continuing the work,’’ whereupon Doctor
Langley requested that arrangements be made for a distribution of the aero-
drome material procured jointly from funds allotted by the Board and by the
Smithsonian Institution. Doctor Langley was informed that all of the mate-
rial would be left in his possession and available for any future work that he
might be able to carry on in connection with the problem of mechanical flight.

That this refusal of the Board of Ordnance and Fortification to render
further assistance to the work was due to the fear that such action would re-
sult in a curtailment of their appropriation by Congress is clearly shown by
the following extract from the official report of the Board on November 14,
1908, to the Secretary of War:

AERIAL NAVIGATION

For a number of years the Board has been interested in the subject of
aerial navigation, and as long ago as 1898 made allotments to carry on experi-
ments with a machine of the heavier-than-air type, under the direction of the
late Dr. S. P. Langley, Secretary of the Smithsonian Institution, who had made
exhaustive experiments in aerodynamics,‘ and who had demonstrated the practi-
eability of mechanical flight by the successful operation of engine-driven models.

The many problems and mechanical difficulties met with in the development
of the full-size machine have been set forth in the various published statements *

1See Experiments in Aerodynamics, Smithsonian Contributions to Knowledge, Vol. 27, Washing-

ton, 1891.
2 Researches and Experiments in Aerial Navigation, Smithsonian Publication No, 1809, Washing-

ton, 1908.

280 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE ViOle|

of Doctor Langley, and the unsuccessful outcome of the experiments is too well
known to require reiteration. It may be said, however, that at the time of the
trials the Board was of the opinion that the failure of the aerodrome to suc-
cessfully operate was in no manner due to the machine itself, but solely to acci-
dents in the launching apparatus, which caused the wreck of the aerodrome be-
fore it was in free flight.

Doctor Langley considered it desirable to continue the experiments, but the
Board deemed it advisable, largely in view of the adverse opinions expressed
in Congress and elsewhere, to suspend operations in this direction.

These adverse opinions expressed in Congress were wholly due to the bit-
ter criticism by the newspapers, whose hostility was engendered by Mr. Lang-
ley’s refusal to admit their representatives to the shops and house-boat where
the work was in progress. Mr. Langley had at all times tried to make his po-
sition in the matter clear to the newspapers, but, on August 19, 1903, at the
time of one of his visits to the experimental station near Widewater, Va., he
found the newspaper representatives so persistent in their misrepresentations
of his reasons for excluding them that he gave out the following statement,
which was published at that time:

SmirHsonran Instirution, Wasutneton, D. C.,
August 19, 1903.

To rue Press: The present experiments being made in mechanical flight
have been carried on partly with funds provided by the Board of Ordnance
and Fortification and partly from private sources, and from a special endow-
ment of the Smithsonian Institution. The experiments are carried on with the
approval of the Board of Regents of the Smithsonian Institution.

The public’s interest in them may lead to an unfounded expectation as to
their immediate results, without an explanation which is here briefly given.

These trials, with some already conducted with steam-driven flying ma-
chines, are believed to be the first in the history of invention where bodies, far
heavier than the air itself, have been sustained in the air for more than a few
seconds by purely mechanical means.

In my previous trials, success has only been reached after initial failures,
which alone have taught the way to it, and I know no reason why the prospective
trials should be an exception.

It is possible, rather than probable, that it may be otherwise now, but judg-
ine them from the light of past experience, it is to be regretted that the en-
foreed publicity which has been given to these initial experiments, which are
essentially experiments and nothing else, may lead to quite unfounded ex-
pectations.

[t is the practice of all scientific men, indeed of all prudent men, not to
make public the results of their work till these are certain. This consideration,
and not any desire to withhold from the public matters in which the public is in-
terested, has dictated the policy thus far pursued here. The fullest publicity,
consistent with the national interest (since these recent experiments have for
their object the development of a machine for war purposes), will be given to
this work when it reaches a stage which warrants publication.

(Signed.) §. P. Laneuey.

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 281

Although it was impossible to immediately find funds for actively continu-
ing the work, the writer finally, after some delay, persuaded Mr. Langley to
allot a small sum from a limited fund which personal friends had some time
previously placed at his disposal for use in any experiments he might wish to
make. This small sum was used to meet the expense of the workmen who
were kept employed long enough to completely repair the main frame so that,
should further experiments be possible at a later time, there would be no dan-
ger of important parts and fittings having been lost in the meantime, and even
if no further experiments were made the frame would be in such condition that
others could profit from an examination of it, the frame itself embodying the
solution of many important problems which had cost much time and money.

In the spring of 1904, after the repairs to the main frame were well under
way, the writer on his own initiative undertook to see what could be done to-
wards securing for Mr. Langley’s disposal the small financial assistance neces-
sary to continue the work; but he found that while a number of men of means
were willing to assist in the development of the aerodrome, provided arrange-
ments were made for later commercialization, yet none were ready to render
the assistance from a desire to assist in the prosecution of scientific work.
Many years prior to this Mr. Langley had had some very tempting proposi-
tions made to him by certain business men with a view to carrying on the work
in a way that would lead to later commercial development. He had never pat-
ented anything previously in his life, and although many friends had urged that
it was only proper that he should patent whatever of value had been developed
in connection with the aerodromes, he steadfastly refused to do so. He had
given his time and his best labors to the world without hope of remuneration,
and he could not bring himself at his stage of life to consent to capitalize
his scientific work. Success seemed only a step away, and his age was such
that any delay in achieving success increased the probability of his not living

to see it, but he maintained positively and resolutely that, if neither the War

Department nor others felt sufficient interest in the work to provide the small
amount of funds necessary to continue the experiments, and they therefore
could be continued only by his giving in and permitting his work to be eapi-
talized, he would have to deny himself the hope of living to see the machine
achieve success.

The result is well known to all.

PRESENT STATUS OF THE WorK

The completely repaired frame of the large machine is now stored in one
of the workshops at the Smithsonian Institution. The large engine, the steam-
driven models Nos. 5 and 6, and the quarter-size model, driven by the three

282, SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL, Di

horse-power gasoline engine, are on exhibition at the U. S. National Museum.
The launching car and a small amount of materials have also been stored away.
The large house-boat, the construction and maintenance of which proved such
a serious drain on the finances, and the preservation of which would have en-
tailed the continuance of heavy fixed charges, has been turned over to the War
Department and sold, as has also the power-launch and other paraphernalia
which it seemed useless to preserve.

The writer is firmly convinced that the aerodrome is not only correct in
principle but that it possesses no inherent faults or weaknesses, and that the
suecess which the work deserves has been frustrated by two most unfortunate
accidents in the laanching of the machine. Other plans of launching, several
of which were studied out during the early stages of the work on the large
machine, would have avoided the accident which did occur, but, of course, might
have produced others possibly even more disastrous, but which could be deter-
mined only by actual trial. But even recognizing certain fundamental weak-
nesses of the launching mechanism as used, he believes that there is no inher-
ent reason why the machine should not have been successfully launched, and
that the accidents which proved so disastrous in the two experiments were not
such as should cause a lack of confidence in the final success of the aerodrome.

It might be of interest to add that the writer is now preparing to resume
the work at the earliest opportunity, and that the machine will be used in prac-
tically the form in which it existed at the two previous experiments, though a
slight change will be made permitting experiments over the land rather than
the water. The only thing that prevents an immediate resumption is the pres-
sure of private business matters.

3efore closing this record the writer wishes to acknowledge the very val-
uable assistance in the work rendered by Mr. Richard Rathbun, Assistant Sec-
retary of the Smithsonian Institution, through his moral support and interest
in it at all times, and especially during the trying days of the summer of
1903; by Captain I. N. Lewis, who, while Recorder of the Board of Ordnance
and Fortification from 1898 to 1902, manifested keen interest in the work and
gave it his moral support before the Board; by Professor John M. Manly, who
devoted the whole of the summer of 1903 to it; and by Professor W. G. Manly,
who devoted a large part of the summer of 1903 to assistance in the prepara-
tion for the actual field-trials of the aerodrome.

Mention must also be made of the very loyal and valuable services ren-
dered by Mr. R. L. Reed, the very efficient foreman of the work during the last
ten years of its progress, to whom much credit is due for his perseverance and
skill in overcoming many of the difficulties which presented themselves, as well
as to Mr. G. D. McDonald, Mr. C. H. Darcey, Mr. F. Hewitt, Mr. R. 8. Newham

no. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 283

and the other employees who labored faithfully for the several years they were
engaged on it.

Bueriot Macuine or 1907 on Lanciey Tyre

Since completing the preparation of this Memoir, the writer’s attention has
been called to some very interesting tests made at Issy by M. Louis Blériot with a
machine of the Langley type. These tests confirm in such a practical manner
the conviction that the large aerodrome would have flown successfully had it not
been wrecked in launching that it has seemed well to here quote an interesting
description of them published in the ‘‘ Bollettino della Societa Aeronautica
Italiana, August, 1907,’’ under the title ‘‘ Il nuovo aeroplano Blériot,’’ a transla-
tion of which is as follows:

THE NEW BLERIOT AEROPLANE

The Blériot IV in the form of a bird, of which we spoke at length in No. 4 of
the Bulletin of this year, does not appear to give good results, perhaps on account
of its lack of stability, and Blériot instead of trying some modifications which
might remedy such a grave fault, laid it aside and at once began the construc-
tion of a new type, No. V, adopting purely and simply the arrangement of the
American, Langley, which offers a good stability (see Bulletin 11-12, November
to December, 1905, pages 187 and 188).

The experiments, which were commenced a month ago, were first completely
negative, because the 24 HP. motor would not turn the propeller, which was 1.80
m. in diameter and 1.40 m. pitch.

By advice of Captain Ferber, Blériot reduced the pitch of his propeller to
0.90 m., so that the motor could give all its force.

This modification was an important one for his aeroplane. From that
moment every trial marked an advance. On July 12, he made a flight of 30 m.,
and the aviator was able to show that the lateral stability was perfect. On July
15, the trial was made against a wind of 6 miles an hour, but gave good results.
He made a flight of 80 m., showing, however, that the hind part of the aeroplane
was too heavy. In this flight he arose as high as a second story, and on landing
the wheels and one propeller were somewhat damaged.

On July 24, repairs having been eompleted, a new trial was made. This
time, in order to remedy the defect in the balance, Blériot had moved his seat
forward about 80 em. The correction was too ereat, for on that day the aero-
plane, although the hind part arose, was not able to leave the ground. On July
97, after having mounted the seat on wheels as skiffs, Blériot resumed the trials
and made a flight of 120 m., at first moving his seat back and then, after getting
: Blériot had not provided this aeroplane with an
elevating rudder, but, following the example of Lilienthal, changed the center of
eravity of the apparatus by moving his own person, and after having ee
the proper angle remained immovable on his seat. In order to arise o1 descend,
the aviator made use of the spark lever, thus varying the number of turns of the

propeller.
During

of the aviation field, Blériot, w

liged to descend, decided to attempt a turn by

started, bringing it forward.

4 second trial on the same day, having accidently reached the limit
‘thout allowine himself to be surprised and ob-
maneuvering the steering rudder

284 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

and to return again to the center of the field. With marvelous precision, the
aeroplane began to describe a circle of about 200 m. radius, inclining as if on a
banked track. Having finished the flight, he quickly regained his balance still in
the direction of the wind, but on account of a slight movement of the aviator,
the aeroplane fell to such an extent that he was obliged to land. He landed
gently and without shock, rolling on his wheels.

~ On Auzust 1, he made another flignt of 100 m. in 6} seconds; and on the 6th,
one of 265 m. with one interruption. While the attention of the pilot was dis-
tracted for a moment, the aeroplane, which was flying at a height of 2 or 3 m.
above the ground, touched the soil with its sustaining wheels at the end of 122 m.
and then immediately arising, covered the remaining 143 m. at a height of 12 m.
Blériot, moving forward too quickly, caused the aeroplane to descend swiftly to
the ground, and the shock broke the axle and the blades of the propeller were
bent. In order to confirm this account, we reproduce what was said in the
“¢ Auto ’’ of August 7, 1907.

‘¢M. Blériot, continuing the trials of his aeroplane yesterday, surpassed the
superb results which he had already obtained. The trial took place at 2 0’clock
in the afternoon on the aviation field of Issy. After a sustained flight of about
122 m. at a height of 2 m., the aeroplane touched the ground, without stopping,
however, and set out again almost immediately at a height of 12 m. and traversed
about 143 m. M. Blériot, who for the time had no other means of balancing but
by moving his body, then moved a little forward to stop the ascent. The aero-
plane plunged forward, and in the fall the propeller was damaged and the axle
broken.

‘« M. Blériot, whose courage as a sportsman equals his learning as an engin-
eer, was fortunately uninjured. An inspection of the apparatus showed that one
blade of the propeller was bent, which was sufficient to prevent the maneuver
made by the aviator having its desired effect and contributed to the fall. The
engine will be repaired without difficulty and the trials will be resumed Friday.’’

On August 10, he made a flight of 80 m., but the motor was not in perfect
order, so Blériot did not make other trials. He decided, however, to substitute
definitely a 50 HP. motor for the 24 HP. motor with which he made all the ex-
periments above reported, which were of a character to encourage the most san-
guine expectations.

Ferber advised Blériot to adopt an elevating rudder also, because the effect
produced by changing the position of the center of gravity, although efficacious
is very difficult and delicate to control.

The conclusion of an article by Ferber in ‘‘ Nature ’’ of August 10, is worthy
of note. He says: ‘‘ Let us remark, in conclusion, how fruitful is the method of
personal trial which we have always advised in preference to any calculation.
This year, with his fourth apparatus, Blériot has not met with any damage to
his aeroplane. He made the trials himself and they quickly led to results, because

each trial gave him an exact idea of what was to be corrected. That is the con-
dition of suecess,’’

——- 9

APPENDIX
STUDY OF THE AMERICAN BUZZARD AND THE ‘‘ JOHN CROW ”’

In the preparation of this Memoir, the writer has deemed it best to generally
omit any mention of plans and ideas which were brought forth in the work, unless
constructions or tests in accordance with them were carried to a sufficient extent
to admit of some definite conclusion regarding them. However, owing to the im-
portant part played by the warping of the supporting surfaces, or the variation
in the angle of auxiliary surfaces, in the methods of preserving the equilibrium
of practically all flying machines of the present day, it may be of interest to here
add a short mention of the direction in which plans along this line were orig-
inally proposed in this work. Mention has already been made of the importance
which Mr. Langley attached to the study of the works of the great master-
builder, Nature, though recognizing at the same time that owing both to the
difference in the forces and methods of construction possible to man, it was not
in general possible for him to produce the best results by attempting to too
closely imitate the methods or plans of Nature.

Mr. Langley considered it not practicable or best to attempt to imitate the
details of construction of the flying mechanism of birds. At the same time, he-
strongly believed that much was to be learned from them about the practical
side of the art of balancing, and he therefore spent a great deal of time both in
analyzing the methods practiced by the birds in preserving their equilibrium and
in criticizing his own plans in this direction in the light of what Nature would
seem likely to do if she had to construct a flying creature on such a large seale.
In carrying on his investigations in the art as practiced by the birds, he made a
trip to Jamaica during the early weeks of 1900, in order to study the species of
buzzard which are so numerous and tame there and are known locally as the
‘¢ John Crow.’’? After his return from this trip he wrote the following very
interesting letter to Mr. Robert Ridgway, requesting certain data regarding the
American buzzard, which he wished to compare with some data on the ‘* John

Crow ”’ which he had obtained on this trip:
Marcu 29, 1900.

Dear Mr. Ripeway:

Thave just returned from Jamaica, where among other occupations, I have
been studying the evolutions of the buzzard locally called the ‘*‘ John Crow,”’ a
soaring bird which is almost as much superior in skill to our buzzard as that is
to a barn-yard fowl in its power of keeping itself in the air without flapping its
wings, in what is very nearly a calm.

T have observed particularly the following points with the Jamaica specimen

(which I can only give, however, approximately), and I should like to have you
give corresponding ones for our Washington buzzard if you can oblige me.

286 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

[ note here that the measurements were made on a live bird and that it was
impracticable to get the separate weight of the wings except by estimate, but the
two wings may be estimated collectively as 1} lbs., the whole weight being 2% lbs.
to 3 lbs.

Approximate values :
Weight of the bird complete, 3 pounds.
Length of bird, 28 inches.
Spread of wings from tip to tip, 5 ft. 5 in.
Complete curtate area of both wings (that is, the area of the shadow of

the bird’s wings when these are fully extended under a vertical sun) is 600

square inches, or nearly 4 sq. ft., consequently each square foot of the bird’s

sustaining surface carries ? lbs. Diedral angle nearly 150°.

When the bird is soaring in a nearly calm atmosphere, which it mexplicably
does,—soaring I mean nearly in the line of the observer’s eyes and coming di-
rectly to or going directly away from him,—it presents nearly the following
appea rance:

Fic. 1.—Jamaica, Mch. 22, 1900. ‘John Crow.’ Sketch soaring horizontally, by W. H. Holmes.
Weight 3 lbs. Total wings area—=546 in. Perpendicular distance c below a b=—3.3 in. =

(5410 — oP, __ 0G.

Fic. 2.—Another.
Vv 546
7
Fics. 1 and 2.—Type sketches of wings by Holmes from a mean of positions taken from his own
sketches and photographs, anu also from sketches and photographs by Langley.

CPI — CG: — 30m De

Fic. 3.—Typé sketch of same birds, average type, position of wings.—S. P. Langley
V546
65m

a b

CP; — CG, — 315) in, —

Fic. 4.—Average typical position of wings in soaring gull. From memory by S. P. Langley. (The
scale here may be taken approximately at ig)

no. 3 APPENDIX 287

I must preface what follows by a little statement of the things which partic
ularly interest me here and which are not a naturalist’s ordinary concern.

First, I want to know the CG of the bird when in flight. You will under-
stand that though there is but one center of gravity (here symbolized as CG), it
may be considered (1) with reference to its position on the horizontal plan of
the bird with wings extended, when it will always be found somewhere in tlie
medial vertical plane, passing through the body, and usually nearly at a certain
point with reference to length, the position thus considered being called CG, or
(2) the position of the same CG with reference to a vertical plane passing trans-
versely through the medial line, the position thus considered being called CG).
In the latter case you will understand that the CG@ which is that of the whole
body, wings and all, will be carried more or less upward when the wings are
thrown high up, and will be carried temporarily downward when the wings are
at their lowest point of the stroke. It would have a certain position when the
bird was at rest and another position when it was soaring and the wings were
above the body. :

The soaring bird is chiefly held upward by the pressure of the air under
each wing, and just as the common center of gravity is a point where all the
efforts of gravity are supposed to be centered, so there is a common center of
pressure, or one point where all the efforts of the upper pressure of the air
may be supposed to be centered, and it will be clear, on very little consideration
that this latter point must be always nearly in a vertical line through the CG, and
usually above it. Call it CP.

CG, and CP, are then, the symbols of CG and CP as referred to the horizontal
plane. CG. and CP, are the symbols for the corresponding ones when referred
to their position in the vertical plane.

I shall be glad to explain to you, if you are not familiar with it, the simple
method of finding the CG, and CG. It consists in bending the wings into just the
position that they would ordinarily oceupy above the body in plain soaring flight,
keeping them there by a very light bent stick or wire, then hanging the bird up by
a line attached to the tip of one wing, and see where this line would pass through
the body of the bird, for the CG will be somewhere in this line. After marking
then, on the body of the bird its position, hang it up a second time by the head or
tail and note again where the new vertical line runs in the new position. There
is but one CG and but one point in which two straight lines can cross, and that will
be the CG necessarily. Note with all care just where this is above or below the
center of the body of the bird.

As for the CP for either wing, that may be nearly found by tracing the wing
on a flat piece of thick paper or cardboard strong enough not to bend much—
cutting out the tracing and balancing it well on the point of a pencil—the point
about which it balances is very near CP, or the center of pressure in the vertical
plane. There is such a point of course in each wing, and when they are thrown
up in the actual position that they have in ealm soaring flight, we may suppose a
horizontal line drawn between them, and it is the distance from this horizontal
line to CG, compared with the area of the wings or with the distance between
their extended tips which we want to know, which gives the vertical distance
which the CG is below the CP, the thing we want to know.

Tt will be very convenient also to have a wing dissected from the body and
the wing itself held in about the soaring curve by a bit of light stick balanced on
a pencil point, which will give the CG of the wing as distinct from that of the
body. However, the three things I principally want, beside a sketch or photo-

288 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

graph of the bird from about its own level coming directly toward or going
directly away in soaring flight, are these:

Approximate weight of the bird—and approximate tracing of its extended
wing with the area, so that we can tell the area of the supporting surface rela-
tive to the weight, and finally, the distance between CP, and CG;, which is obtain-
able by the process which I have explained.

Lam afraid that what I have just been describing at such length may have a
certain obscurity to you, but if you will give me an opportunity, I shall be pleased
to illustrate it with the actual experiment when the bird is hung up by a string,
and you will see that it is in reality simple.

Referring to the sketches on page 3 of this communication, a and b corre-
spond to the centers of pressure on either wing where the upward pressure of the
air distributed over each wing may be supposed to be gathered in a single point.
This, as I have said, is called the center of pressure with reference to the vertical
flight, and its symbol is CP., while the horizontal dotted line between them repre-
sents the level of CP. from the best estimate that I could make when the wings
are in their natural position of soaring. It is evident that this line passed far
above the body of the vulture, and if (the corresponding symbol for the height
of the center of gravity being CG.), the CG, of the entire bird be taken, it will
be found to lie nearly in the point c. Where ¢ is in the present case, I could not
determine exactly in my hasty examinations in the live bird, but I assume that it
is about 4 way between the central horizontal axial line of the bird’s body and
the upper portion. I repeat that it is important to me to know what the vertical
distance is between CP, and CG, in each specimen of soaring bird. I may ob-
serve in illustration that in the common sea-gull, it is nearly as shown in the faint
sketch; that is to say, that the corresponding line a b in the soaring gull passes
distinetly through the upper part of the body, and the distance down to the CG, of
the whole in the gull is almost nil, while in the buzzard it is very considerable
as shown by the corresponding distance in the ‘‘ John Crow.’’

Now, what I want to get from you is the corresponding figures for an aver-
age specimen of our Washington buzzard. If you will kindly have one killed and
weighed while fresh, and before the rigor-mortis has set in, first noting the posi-
tion of its wings when soaring in a calm, and (if possible) when coming toward
you or going away in about a horizontal plane with your eye, in which position
the wings will be elevated and bent somewhat as in the case of the above sketch
of the ‘* John Crow ’’; if you will kindly do this, so as to give me corresponding
facts with reference to the buzzard, namely weight, area of extended wing sur-
face, distance between tips as bent up in ordinary flight, distance between e2-
tended tips, the quantity CP.—CG., and also will make such a tracing of the buz-
zard’s wing as Mr. Manly will show you of the ‘‘ John Crow’s,’’ I shall be
obliged.

My impression is that the buzzard is a considerably heavier bird than the
‘John Crow,’’ without, however, very much greater spread of wing. I may
observe that when the wings of the Jamaica bird were spread out, they were
spread quite to their utmost extent, and the distance between the tips of the
terminal feathers was much greater than when in flight. I wish you would
kindly also add the scientific name of the ‘‘ John Crow,’’ with any particulars
that you would think of interest.

If there be any special expenses incurred in the preparation of this mem-
orandum, including the time of a photographer, I will direct them to be paid
from the Smithsonian fund.

NO. 3 APPENDIX 289

If you could get Mr. Holmes (who made most of the sketches and all of the
photographs of the ‘‘ John Crow ’’), to try and do something like this for your
buzzard, especially getting such a photograph of it in flight, as will give the posi-
tion of its center of gravity relative to the center of pressure on the wings, it
would add very greatly to the value of your memoranda, and [ think Mr. Holmes
takes so full and intelligent an interest in the subject, that he might be pleased
to give his help.

Very truly yours,
S. P. Laneiey,
Secretary.
Mr. Roserr Rineway,

Smithsonian Institution,

Curator, Division of Ornithology, U.S. National Museum, Washington,

DAC:

In response to this request, Mr. Ridgway submitted the following very inter-
esting information:

SMITHSONIAN INSTITUTION,
Unirep States Nationa Museum
Wasuincton, D. C., October 16, 1900.

Pror. S. P. Lane ey,

Secretary, Smithsonian Institution.
Sir:

T have the honor of submitting herewith the data obtained by Mr. Rolla P.
Currie concerning measurements, ete., of the common Turkey Buzzard (Cathartes
aura) of the United States, as requested by you in your letter of March 29, last.

The difficulties in the way of securing these data, already explained by me in
previous communications, are responsible for the delay in submitting them.

Hoping that this material may prove of use to you, J. am,

Very respectfully,
R. Ripeway,
Curator, Division of Birds.

Memoranpa tn Recarp To THE TurKEY Buzzarp (SECOND SPECIMEN)

1. Weight.—1850 grammes.
2. Area of outstretched wings.—641 square inches. (Computed from three
sheets of tracings, 4, and A, comprising the entire area of both wings; b, a

single wing.
to) 5 ; ;
Note.—As the bird was in process of moult, one of the large wing quills, as

shown by the tracings and compo-board patterns, is but partially developed,

thus slightly modifying the results obtained. Its length, if full grown, would be

nearly the same as that of the quill just above it.
3. Distance between the tips of these wings.—» feet, 8.7 inches.

4. Distance between the tips of the same wings when the bird is in horizontal

: ae i 5 ; : 71 a 4a Ye)

soaring flight—Kstimating the dihedral angle of the wings to be 150°, and
ing t e, the distance between their tips

elevating the wings sd as to make this angl
33

990 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

measures 5 feet, 5.7 inches, or 3 inches less than when fully extended in the hori-
zontal plane.

5. The position of the center of pressure of the wing.—This is indicated on
two compo-board patterns, C and D. C was made from a fully extended wing,
while D was made from the wing in the soaring position. The centers of pressure
of the wings are about 2 feet, 0.5 inches apart, or 1 foot, 0.25 inches from the
central point of the bird’s body.

6. The position of the center of gravity of the soaring bird.—(Length of
buzzard, 26 inches.) The center of gravity of the soaring buzzard in the hori-
zontal plane, CG,, was found to lie 93 inches behind the tip of the beak and 163
inches in front of the tip of the tail.

The center of gravity of the soaring bird in the vertical plane, CG., was
found to lie 2.8 inches above the ventral point of the body and 1.6 inches below
the dorsal point, the depth of the bird’s body at CG, being 4.4 inches.

In determining the center of gravity, the bird was frozen in the soaring
position, its wings making a dihedral angle of 150°. It was then hung up, first
horizontally and then vertically, and balanced till the line from which it was sus-
pended coincided with a plumb-line placed in front of it; the measurements were
then made.

The bird was afterwards, and while still frozen, hung up in the same way
in Mr. Smillie’s photographic room, and exposures made by him in both posi-
tions. These photographs, HZ, and F’, were enlarged to natural size, and meas-
urements made on the enlargements yielded, as nearly as could be determined,
the same results as when taken directly upon the bird.

As determined by measurements upon the buzzard in soaring position, the
center of gravity was found to be 2.65 inches below the center of pressure (esti-
mating the center of pressure to be at the bend of the wing); or, employing the
compo-board pattern in a corresponding position, the distance was seen to be a
small fraction of an inch less.

7. The position of the root of the wing.—This is indicated on the tracing A,.

a. (Depth of the body on a vertical line with root, 3.5 inches.) The root lies
1.6 inches below dorsal line, 1.9 inches above ventral line.

b. (Length of body, 26 inches.) The root lies 7.6 inches behind tip of beak,
18.4 inches in front of tip of tail.

8. The dihedral angle between the wings—The photographs taken previ-
ously were not sufficiently large or distinct to enable us to determine this with
exactness. It was estimated, however, as 150°, and experiments were made on
this basis.

9. The center of gravity of the dissected wing—This was found, first, for
the wing having all the muscles, up to the ball and socket joint, intact. One of
the wings was frozen in the soaring position and its center of gravity found by
balancing on a point. Its position was marked by a wire thrust through the
wing at this place, and the wing (H) is preserved in formalin. This position
is also marked on a special tracing, J. It lies 6 inches from the base of the
humerus bone (root of wing). Secondly, it was found for the wing denuded of
all muscle. Its position was marked on the other wing of the bird, which is pre-

served dry, spread in the soaring position. It lies 9? inches from the base of the
humerus.

no. 3 APPENDIX 291.

10. The weight of the dissected wing.—

a. With all muscle up to the ball and socket joint intact, 325 grammes.

b. With all muscle removed, 190 grammes.

Weight of muscle, therefore, 135 grammes.

The position of the root of the tail—

a. In the horizontal plane, 11.8 inches in front of the tip of the longest tail
feather; 14.2 inches behind tip of beak.

b. In the vertical plane: (depth of body from ventral point below root of tail
to a point directly above, which is on a level with the highest point of the back,
2.5 inches.) 1.5 inches above ventral point, 1 inch below dorsal point.

Weight of tail—With muscle, 40 grammes; without muscle, 30 grammes.
Weight of muscle, therefore, 10 grammes.

EXHIBITS ACCOMPANYING THESE MEMORANDA

Exuisir E,.—Turkey Buzzard suspended in soaring position. (R. P. Currie.)

A, and A;. Two sheets, comprising a tracing of the entire turkey buzzard
with fully outstretched wings. From these the area of the wings and the dis-
tance between their tips was obtained. The position of the root of the wing and
the root of the tail is also marked on one of these sheets.

B. One sheet, comprising a tracing of a single wing, and from which the
area was also computed. This area, multiplied by 2, gives the same result as the
sum of both wings on A, and A,. The compo-board pattern C was made from this
tracing.

C. Compo-board pattern of fully extended wing, on which the center of
pressure is indicated.

D. Compo-board pattern of wing in soaring position, on which the center
of pressure is shown.

92 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

bo

E,. Photograph of bird in soaring position, suspended horizontally.
Same, enlarged to natural size.

F,. Photograph of bird in soaring position, suspended vertically.

F.. Same, enlarged to natural size. 2

G. Tracing of wing in soaring position, from which the compo-board pat-
tern D was made.

Exuisir F,.—Turkey Buzzard suspended vertically in soaring position. (R. P. Currie.)

H. Wing preserved in formalin, on which the center of gravity is recorded.

I. Tracing of wing H when frozen in soaring position, on which the center
of gravity is marked.

J. Wing with muscle removed, on which the center of gravity is shown.

Several persons connected with the Smithsonian Institution and U. 8. Na-
tional Museum have contributed towards securing the results herewith sub-
mitted. Among them, I desire especially to mention Mr. W. H. Holmes, Mr.

No. 3 APPENDIX 293

I". A. Lucas, Mr. N. R. Wood, and Mr. R. L. Reed. Mr. Holmes superintended
the experiments in connection with No. 6 (finding the bird’s center of gravity),
and by his suggestions and criticisms helped me in many other particulars. The
photographs and enlargements were made by Mr. T. W. Smillie.

Respectfully submitted,

Rotua P. Currie,
Aid, Division of Insects, acting in the Division of Birds.
Ocroser 16, 1900.

The feats of airmanship performed by the ‘“‘ John Crow ’’ seemed to greatly
impress Mr. Langley and shortly after this trip he wrote the following letter to
the writer:

SMITHSONIAN INSTITUTION

Wasninaton, D. C., April 16, 1900.
Dear Mr. Manty:

I am reminded of the consequence that I-have, in connection with Mr.
Chanute and perhaps Mr. Huffaker, attached in the past to the possibility of
directing the bird, and consequently the flying machine, by the mere inflection of
the wing, that is, by changing its angle; and you recall to me that Mr. Huffaker
at one time proposed to arrange a wing, with some provision of a spring, which
should enable it to change its angle automatically. ....

I have been noting this ability to guide by the slight inflection of the wing,
in my studies of the Jamaica buzzard, and am ready to say that I think, while
the quarter-sized working model of the great aerodrome is building, it will be
worth while to make some arrangement of the frame or wing-holder which will
make it possible to test this idea. I will endeavor to work out something of the
kind more in detail myself, but whatever it is, it will apparently involve the
ability of the wing to rotate about a line passing nearly through it lengthwise,
and an allowance for this; if not in the wing itself, then in the wing-holder;
will need to be made while the present model is under construction.

T will request you to especially look out for this, as far as you can on these
indications.

Very respectfully yours,
S. P. Lanc3ey,
Secretary.

The instructions and suggestions contained in this letter and in many con-
ferences on the subject were never carried out by the writer, on account of the
extreme pressure of the work already on him which had for its object, not the
production of a flying machine which would embody all of the control which we
wished it to have, but which would be burdened only with such devices and
arrangements as would enable it to transport a human being, and thus demon-
strate the practicability of human flight.

294. SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

SECRETARY LANGLEY’S INSTRUCTIONS TO ASSISTANTS

Smrrusonian Institution, Wasutneton, D. C., November 30, 1895.

Dear Sir:

The following instructions are to replace those of May 13, 1895:

1. The minimwn fraction of its own “ flying weight ’’ (that is, weight com-
plete with initial water and fuel), which the aerodrome shall lift on the pendu-
lum, is 50 per cent,’ under such engine power as can certainly be gotten up in the
field and maintained during forty seconds from the time the aerodrome is let go.

The blast, the pumps, and all other essential parts must, in other words, be
in such a condition that steam enough for this lifting over 50 per cent of weight
ean be gotten up readily and surely in the field and in a time which will still
leave at least forty seconds’ supply.

9. The minimum relation of supporting area to weight in any aerodrome
constructed hereafter, is to be two feet to the pound, and the minimum of power
at the rate of one steadily-maintained horse power * at the brake under ordimary
conditions, to not over twenty-two pounds (ten kilos) of flying weight. In
absence of a brake determination horse power may be taken—

H. p. —2evs- per min. at rest pitch diameter (in ft.) thrust (in Ibs.)
saat 33,000

These rules do not apply to No. 5, but they do to No. 6, which is to be built over,
if necessary, to meet them.

3. In balancing an aerodrome, unless otherwise instructed, set wings at a
root angle of either 10°, 7°, or 5°, after being certain from previous inversion and
sanding, that the tip angle in motion will not differ from this root angle as much
as 5°.

The object in balancing any aerodrome with a single pair of wings is to be
able to bring the c g. under their ¢ p, without any reference to the tail, which
supports nothing, unless specially ordered. But as this condition cannot now be
obtained in Nos. 5 and 6, these at any rate, and perhaps future aerodromes, are
to carry a second pair of wings. When this second pair of wings is of nearly
equal size with the first, it is to be assumed, in preliminary adjustments for
weight and center of pressure, that the second pair has two-thirds the lifting
efficiency per unit area of the first.

Calling the whole distance from the mean center of pressure of the wings
to the center of gravity M. M is to have a definite relation to the breadth of

2 All these minimum permissible conditions are connected by the tacit assumption that the sup-
porting area is not greatly over 2 ft. to the pound of weight. If for instance the weight were in-
creased by larger wings or more wings, furnishing a much greater supporting area per pound, these
conditions would not necessarily apply.

a fA eee eee |

No. 3 APPENDIX 295

wings from tip to tip (b) and total fore and aft length (1), which is provisionally

fixed at M—V. bb and the line of thrust is to be not over one-fourth the way
from c p, to ¢ g:.

Generally speaking the front pair of wings will be fixed in position and the
adjustment for balancing made by moving the rear pair.

The individual weights of ali parts checked by lump weighing are to be given
by the caretaker (Mr. Huffaker), under the general scheme shown in the note.
The work on the aerodromes being divided into two classes, viz.: metal work and
all which is not metal, the two in charge of this work (Mr. Reed and Mr. Maltby)
are severally responsible for knowing the weight in grammes of any of the parts
they have put into their work, giving these weights to Mr. Huffaker, together
with any data for filling out the annexed tables,’ on his request.

Until further orders, Mr. Huffaker is charged with the responsibility of
seeing that these conditions are met before any aerodrome is boxed, and will keep
the record of weights of the aerodromes.and their principal parts as already com-
pleted, in a book, to be preserved in your keeping, which will also be arranged to
show with signed photographs and descriptions, and with sketches where needed,
the condition and weight (as far as constructed) of every aerodrome, and of any
new construction of any part, on the first of each month.

Particular attention is directed to the preceding paragraph, and to the need
that evidence of a definite character is to be obtained and preserved of every-
thing already done, and being done.

Without special orders to the contrary, you will not authorize the boxing of
any aerodrome which does not, to your knowledge, meet these conditions.

Each aerodrome is to have the following parts in duplicate or in triplicate:

2 pairs wings;

2 pairs tails;

2 pairs light silk covered rudders ;
3 pairs wheels;

with any other parts in duplicate or triplicate, which experience has shown to be
necessary.

Mr. Reed will not box any aerodrome till a certificate from Mr. Huffaker can
be put on the inside cover, with the list of contents, showing what the conditions
are as to weight, wing area, power, ete., and the person in the field charged with
the duty of launching the aerodrome (at present Mr. Reed), is authorized not to
let it go unless he is satisfied that it has a full forty seconds’ supply of steam.

1These tables were later designated as “ Data Sheets.” Several copies, with the data duly
entered on them, are given in this appendix, and the form which Mr. Langley included in this letter
is therefore not repeated here—Ep1ror.

296 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

Iam satisfied that a great deal of time is lost in putting the aerodrome to-

gether for flight, owing to the absence of any preliminary drill in doing this.
3efore it goes into the field the whole is to be completely boxed, and then taken

out from the box and set up on the clutch, and steam gotten up for flight. All
this is to be done in the shop before the final boxing, and provision is to be made
so that no wiring or adjusting of parts is to be done in the field which can pos-
sibly be avoided by forethought in the shop. The tail-piece, for instance, is to be
bushed with brass, so that it will always come into the same place, and make a
tight fit, in spite of wetting or shrinking, in the steel tube, where it is to go into a
guide-way with a bayonet spring, or a like contrivance for setting it at once
securely into position.

The mean positions of the wings and tail are to be laid out in some way
permanently on the mid-rod, but every guy-rod or adjustable piece is to be ar-
ranged so as to fit at once securely and permanently in its position without wiring
or like slow process.

Very truly yours,
S. P. Lanenry,
Secretary.
W. C. Wrntock, Esaq.,
Assistant in Charge,
Smithsonian Institution.
A copy to be communicated to:—Mr. Huffaker,
Mr. Reed,
Mr. Maltby.

ve Sa 6 he noe So * wo

APPENDIX 297

DATA SHEET No. 1.
Weight of Aerodrome No. 5, as photographed on May 11, 1896.
Certified to by R. L. Reed, May 6, 1896.

Parts. Sizes. Weight. Remarks.
|
|
Metres. Feet. Grammes.| Pounds,
1 Frame, including everything of metal, permanent and } Front end of bowsprit, 1586.3.
undetachable, such as_ bed-plate, cross-rods for the
support of propellers, bearing points for clutch, ete...... aie 2443,
2 Bngine, gears, shafts, etc... 22... 0. see e sce nnessccciees 1110 front end of midrod, 1611.6.
3 Pump, pump shaft....... 231
4 Hull covering Reais 850
5 Gasoline tanks, valves 178 Front edge of F. W., 1607.
6 Smokestack 342
ME WIOA TE eset ies 275
8 Reel QQoooséSoosapsasourcasaaE TT | C. of P. on F. W., 1575.
9 Wing clamps, 235; clamp for gu 264
10 Other things, counter.... 7
11 Burners .. oe 360 Back edge of F. W., 1527.
IL} GSR ac 6 Se aReR dase OB ea BORO MUnAES ae 651
18 Separators, steam gauge, pipe to engine. 540.
ne DATES [Oh ooonendootdkonouepenucgod 148 Back edge of cross frame, 1509.
Gis
Lamvnniese Gwibhorte Clamp). cieisceleiscls(sisters ceisic sinieisiisia wcrc x'cialsie vl] weleoeisinis|(sleleielalme 1950 | Line through center of propellers,
18 Tail (without clamp).... 1500.
1) ISG GE? “cB asadanesvectss 350
20 Guy sticks, each, 57 eel 114
GAl Loxapeeilitie) Son6necupecocdn ber cap bbbe qsepsubes Cope eDScscoenon ime 800 C. of G., 1497.
22 Extra length of midrod, 308; drop piece for rudder, 40....|.. 348
23 Wood bowsprit - 5 74
Yront edge of R. W., 1415.5.
26 ae x
27 Fuel (at starting flight). El llajatsterercterel eitisiaree tate 200 @. of P. on R. W.,, 1383.5.
3 Water (at starting flight) 900
| | End of midrod, 1360.5.
ate Front end of rudder, 1343.8.
Al Gore -con lacéoacos 11,775 | 26
| Back edge of R. W., 1835.5.
88 Total area of support (not including tail)........... ite) jeateses 68
89 Total area of support in feet, divided by total flying Center of rudder, 1288.3.
CLS Def emiTiga) Dasa ear eclietetete ta ciiwicketaicielvalcteimelate’stcinl=fatel(otmielet|{a)pinistaisiele 2.6
40 Total area of horizontal tail
41 Total area of rudder (vertical) Aece mae as 6 Back end of rudder, 1229.8.
42 Horse-power at brake.... Horse-power by formula * .72...|-.<-++++ ve
43 Minimum pressure during 40 secs. lift, 150 Tbs.
44 Lift at pendulum (during 40 secs. absolute) 5772....
45 Lift at pendulum (during 40 secs. in terms of wt.) 49%....
46 Minimum pressure with which wheels turn, 10 Tbs.......
47 Position of center of pressure of wings7 F. W.,
URSA Nery wei GOS: oo strai et otatelsieic[sloloielejeistefelole'=in)(oe|siai=/hielsleiniajeielainolsiolelmies
a Time of getting up full steam, 1 minute
50 Curvature of wings, 1/1i.
51 Root angle of wings, 9°.. fae
52 Tip angle of wings, 9°...........:.-eceeeee sere e see eteseres
58 Position of wings, Front rib on F. W. 2 415.5
RA Tate? (abn (as) oggncosodasHeonerbeogecde ;
a} aeedcoe seeeS
56.
Ht! csnsconeceocnames
58 Position of tail.
59 Angle of tail we

60 Co-efficient elasticity of tail.
61 Position of rudder, center, 12!
62) Tine of! thrust; 2500. 2. nnn cece nee nenvcecsesnscioss
68 Line of thrust, 1500 which is 9 em. below the center of
midrod ee c
64 Center of gravity: of whole, 1497
65 Center of gravityz, 2501, i. e., 1 cm. above line of thrust....
66 Center of pressure; of whole estimate, 1498.......----
67 Center of pressures, 2536........++-++-0eeee

*H _ Rev. x diam. x pitch ratio x thrust
bE 33000

+ This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet pet
minute is in ordinary curved wings ¥-5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
efficiency per surface of the front ones and that the tail proper bears no part of the weight; but if rear wing is smaller or larger
this efficiency is smaller or larger per unit of surface.

298

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

DATA SHEET No. 2.
Weight of Aerodrome No. 6.
Certified to by R. L. Reed, November 27 and 28, 1896.

Parts.

Sizes.

Weight.

VOL.

Remarks.

OMI oie oD

30
31
32
33
34
35

SOae

37
38
39

40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56

57 ..

58
59
60
61

62

63
64
65
66
67

68 .
69 .
GU San
all Re

12

Frame, including everything of metal, permanent and
undetachable, such as bed-plate, cross-rods for the
support of propellers, bearing points for clutch, etc......

Engine, gears, shafts, etc. ehasetenrecane

Pump, pump shaft

Hull covering

Gasoline tanks,

Smokestack, 302; burner,

Float

Reel

Wing clamps, 238; drop piece for rudder, 40..

Other things ......-. 5

Boiler, frames, mica cover...........

Separator, steam gauge, pipe to engines.

Exhaust pipe ..

Wings (without clamp), wet.
Tail (without clamp)........
Rudder
Guy sticks, each 53.
Propellers
Extra length of midrod
Wood bowsprit. 4
Counter ....

Puiel (at starting flieht)..
Water (at starting flight).

Sundries unknown ..

Total flying weight

Total area of support (not including tail) q
Total area of support in feet, divided by total flying

WEIGHT an pl Sheena eeniseaiaisia aloe oestalsicieleleteien iar eee eee :

Total area of horizontal tail...
Total area of rudder (vertical)
Horse-power at brake.... Horse-power by formula
Minimum steam pressure during 40 sees. lift...
Lift at pendulum (during one minute absolute).......
Lift at pendulum (during one minute in terms of wt.)
Minimum pressure with which wheels turn............
Position of center of pressure of wings 7...
Time of getting up full steam, 75 secs...
Angle of midrod with horizon, 2° 17’........
Curvature of wings, 1 in 18, %4 from front.
Root angle of wings, 10° 30’...............-
Tip angle of wings, 10° 30’...

Position of wings..........
How guyed

emeCeat us
sq. ft.

Position of tai
Angle of tail....
Co-efficient elasticity of tail
Position of rudder...........

Center of gravity;
Genteriofigravitya,, 2480) ta-eeeem sree ree
Center of pressure; of whole estimate, 1487.
Center of pressures, 2520

of whole, 1483.8. .

Grammes,

1178
1043
190

12,120

Pounds. 7
Front end of bowsprit, 1707.

27

Center of float in first trial, Nov.

27, 1670.

Front end of midrod, 1618.7.

Front edge of F. W., 1595.7.

Center of float in flight, Nov. 28,

1896, 1575.8.

C. of P. on F. W., 1563.7.

Back edge of F. W., 1515.7.

Line through center of propellers,
1500.

C. of G., 1484.4 (old C. of G.,

1486.3).
Front edge of R. W., 1406.
C: of PB. on R. W., 1874,
End of midrod, 1351.3.
Front end of rudder, 1334.5,

Back edge of R. W., 1826.

130
7.211

10

Center of rudder, 1279.

Back end of rudder, 1220.5.

rectangle.
Weight in shop, 1982 g.

On day of flight they

Area 54 sq. ft.

Spread of wings,

11’ 934”.

Weight of aerodrome
12,120 grs.

359 ems.

Reed wings, 8) cm. x 185 cm. in

weighed
2154 g. because they were damp.

or

in flight,

minute is in ordinary curved wings
efficiency per surface of the front on

*H. P. =

32000

Rev. x diam. x pitch ratio x thrust

+ This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per

this efficiency is smaller or larger per unit of surface.
This is undoubtedly incorrect, as if it were true, the C. G. would be just at the center of the separator, and this would be

impossible, Mr, Reed states that the C. G was 2 cm. below the side frame, and if this is correct, we would have C. G.

2

5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
and that the tail proper bears no part of the weight; but if rear wing is smaller or larger

486.

as _ ~~. 7 a BO Wis pons - nl ———ae ee

APPENDIX 299

DATA SHEET No. 3.
Weight of Aerodrome No. 6, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, June 7, 1899.

Parts. Sizes. Weight. Remarks,
isa ail - Metres. Feet, Cranmer Pounds,
ame, including everything of metal, permanent and Front i 702.7.
undetachable, such as bed-plate, cross-rods for the Sees ecg eT
support of propellers, bearing points for clutch, ete...... | f 2867
2 Engine, gears, shafts, etc.............. manetetaleleleieratete eal} U Center of float with small wind
3 Pump, 123; pump shaft, 49.......... Meistaeces peiienitecceee 1i2 vane rudder, 1628.9.
4 Hull covering, including apron and piece behind separator. arid coe 274
5 Gasoline and air tanks, 167, 114; air valve, 16............ a5 4\|SooniGans 297
6 Smokestack, 319; counter, 95; burner, 165. 679 | * Front edge of midrod, 1613.7.
7 Float, 275; pipe from pump to boiler, 40 316 :
8 Reel, with fork and float............... 128
9 Wing clamps, 188; guy-post clamps, 24...... 212 Center of float with smal! rudder
10 Boiler, 764; steam gauge and connections, 79....... ae 843 off, 1609.2.
11 Front lower bearing post, 75; clutch post, 58; rear bearing
mokicy LL cosdoe sooadonasoun soscipdoopbanscoocnussbanaooe. 288
ae Front edge of F. W., 1595.7.
MOREE ANN ENE EN Fen Resid sn cigs cc sn nacotictenera o@ :
a8, ¢ Cc. of P. on F. W., 1563.7.
17 Wings (without clamp). Bal aaa 3 ae clip OTT
18 Superposed wings, 3448 Back edge of F. W., 1515.7.
il) 0GCGES nodeosinesuede Bolles 323
20 Guy sticks, each 53. 3h 50 106
PANPTOPeMeTa)s <lemeiececn sie 620 Line through center of propellers,
22 Extra length of midrod. 317 1500,
23 Wood bowsprit.......... 128
24 Canvas keel, 36; rudder, 76 112
AS sogasaacdoogdeousoLdeoNd C. of G., 1484.4.
13 Sag asophanoapaspoonEOeen
27 Fuel (at starting flight)... Bosna <Hlocabesoa 175 F .
DRE Watered (AL StALtine Ment) |armiscieececlsloceitceete rea voi ciseecta se] sees eaed ans 1525 Front edge of R. W., 1406.5.
C. of P. on R. W., 1374.5.
alles .see-{ 11,995 | 26.44 | End of midrod, 1351.8.
if Front end of rudder, 1335.
88 Total area of support (not including ay) sEaeDCOsOSS m6 10S ogoenecd 54
89 Total area of support in feet, divided by total flyin
weight in Ibs ite on = a ON Od ceaoes Back edge of R. W., 1326.5.
40 xate area of horizontal ta aK “ eae
41 Total area of rudder (vertical)..............ses-eeee~ vi “5 a
42 Horse-power at brake.... Horse-power by formula *. Center of rudder, 1279.5.

44 Lift at pendulum (during one minute absolute)

45 Lift at pendulum (during one minute in terms of wt.).... Back end of rudder, 1221.

46 Minimum pressure with which wheels turn...............-+
47 Position of center of pressure of wings f 40% from front...

eine rss

51 Root angle of wings, 10°....
52 Tip angle of wings, 10°...............+5- 5008 oper
58 Position of wings—front edge of front wing, 1595.7; of
PCM MIE sy BLOG soto ele iaratalnlai=\olalelesele ele) atorsts|etel=twlciwceref=isinia/ole mre .a/a

54 How guyed—with wires from wing to wing on top and
to guy-post on bottom Ba00

bf 1 shSeSn cos soconcaudeEc BeUsueDoOe

58 Position of center of rudder, 127
59 Angle of tail, 10°...........
60 Co-efficient elasticity of tail..
61 Position of rudder...........

GP snctgnnpodosdncemageos
68 Line of thrust, 1500.............---
64 Center of gravity, of whole, 1484.4
65 Genter of Pravilye......26 cs ewecccaver
66 Center of pressure; of whole estimate. .
67 Center of pressures

Rev. x diam. x pitch ratio x thrust
33000
+ This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per

minute is in ordinary curved wings 2-5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
efficiency per surface of the front ones and that the tail proper bears no part of the weight; but if rear wing is smaller or larger

this efficiency is smaller or larger per unit of surface.

*H. P. =

300 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOLseci

DATA SHEET No. 4.
Weight of Aerodrome No. 6, Superposed Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, June 13, 1899.

Parts. Sizes. Weight. Remarks.

Metres. Feet. | Grammes.| Pounds.

1 Frame, including everything of metal, permanent and Front end of bowsprit, 1702.7.
undetachable, such as bed-plate, cross-rods for the
support of propellers, bearing points for clutch, etc......|--

STEN PINE: PEATE BAITS, CLC lets cleinicteinlererelsierelernicielelai= 4

3 Pump, 123; pump shaft, 49..........

4 Wull covering, including apron and piece behind sepa

5 Gasoline and air tanks, 167, 114; air valve, 16..

6 Smokestack, 319; counter, 95; burner, 170........

7 Float O00

8 Reel, with fork and float.............. 128 Front end of midrod, 1613.7.

9 Wing clamps, 188; guy-post clamp, 24........ Soa bone ad 212

10 Boiler, 764; steam gauge and connections, 79...........---| «+ seselecacoees 843

11 Front bearing point, 75; clutch post, 58; rear bearing Front edge of F. W., 1585.
points, 155 Sea|!0 7

12 Separator and pipes to engines and pump.

18 Drop piece and guy-post for rudder....

ORB7

} 2867 Center of float without small wind
liz vane rudder, 1666.1. (Center of
274 float with wind vane rudder on,
297 1627.)
584
B15

75 C. of P. on F. W., 1563.7.

Rear edge of F. W., 1531.7.

s (without clamp), 2077; superposed wi

eA seectes Sonus 3448
18 Tail (without clamp) ee 5
ADER I derlbarcatetesmateteetsi oe Bee| ccc onnsllicen.cocs 323 Line through center of propellers,

20 Guy sticks 106 1500.

21oPropéelierst ssc. seee ce ecee 620

22 Extra length of midrod 317 {
23 Wood bowsprit . 4 4A 128 C. of G., 1484.4.

24 Canvas keel, 36.. tecallcsaeseh Bl Sonenoe 36

26

ngs..

BsI0o0 AoRG ae Front edge of R. W., 1395.8.
27 Fuel (at starting flight). . nilanneadcollodac cos 175 : ;

28 Water (at starting flight). eiein | malestere del outers 1525
BO a ee ms C. of P. on R. W., 1874.5. ;

End of midrod, 1351.8.

eepadol|oasanoas)| LHL)

34 Total flying weight.

Front end of rudder, 1335,

85

38 Total are P sluding tail). ...:s. ss. Sqiiftllt seetese 87.4 - Back edge of R. W., 1342.5.

q
39 Total area of support in feet, divided by total flying
weight) in-fibssce se commute
40 Total area of horizontal tail.
41 oe area of rudder (vertical) 4
42 p~ Seles - 7 "i GOO
3 orse-power at brake Horse-power by formula Back endilof mudderwio218 :

i aaderiad 9.5 Center of rudder, 1279.5.
7.7 f

44 Lift at pendulum (during one minute absolute)......
45 Lift at pendulum (during one minute in terms of wt.)....
46 Minimum pressure with which wheels turn..............-.-

AG Position of center of pressure of wings +, 40% from front. . ;
49)...
i) Curvature of wings, 1 in 18.
51 Root angle of wings, 10°.....
b2)Tipvanglevof/iwinge: 10s se. cs cee ecasenenle
53 Position of wings—front edge of front wing
54 How guye

al

58 Position of ta 5
BO Ample: Ghitail71Ggsse a occ. soe eee cc eee eee
60 Co-efficient elasticity of tail, 1240 grammes at center to
deflect to the horizontal
61 Position of rudder.
(i) SatmoconpgauocEooneS
63 Line of thrust, 1500..............
64 Center of gravity; of whole, 1484.4
65: Center of gravitys.....2.--cscsudeccans
66 Center of pressure; of whole
67 Center of pressurés...........
Gh} Beconsocaaodos
Gore
70.
(als

Rev. x diam. x pitch ratio x thrust
33000

. 1 This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per
minute is in ordinary curved wings 2-5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
efficiency per surface of the front ones and that the tail proper bears no part of the weight; but if rear wing is smaller or larger
this efficiency is smaller or larger per unit of surface.

*H. P. =

1 Frame, including everything of metal, permanent and
undetachable, such as bed-plate, cross-rods for the
support of propellers, bearing points for clutch, etc.;
GOOWEDISt sl SE iictcieiercraistcle tote cisietcterehaist sielslers

2 Engine, gears, shafts, etc....

3 Pump, 123; pump shaft, 49..

4 Hull covering, including apron ar

5 Gasoline and air tanks, 167, 174; air valve, 16..

6 Smokestack, 319; counter, 95; burner, 170..

7 Float

§ Reel, with fork and float

9 Wing clamps, 188; clamps for guy-posts, 2

10 Boiler, 764; steam gauge and connections, 7

11 Front bearing post, 75: clutch-post, 58...

12 Rear bearing points

13 Separator and pipes leading to engines and pump.

a

gs E
18 Tail (without clamp)
TORR NG der ieee ce cecieiee lie
20 Guy sticks .
21 Propellers
22 Extra length of midrod.
23 Wood bowsprit ....
24 Other things ....
25
26 .. rosdes
27 Fuel (at starting

38 Total a of support (not including q. ft.
89 Total area of support in feet, divided by total flying

ET ONIN RINMEA IS cteters sic atctass/oictsteleseloiulsle’atelcje sisi /feiafaicialdls
40 Total area of horizontal tail. .
41 Total area of rudder (vertical)
42 Horse-power at brake.... Horse-power by formula *......
44 Lift at pendulum (during one minute absolute)... .
45 Lift at pendulum (during one minute in terms of wt.)
46 Minimum pressure with which wheels turn
47 Position of center of pressure of wings +, 40% from front..

50 Curvature of wings, 1 in 1S..
51 Root angle of wings, 10°...

52 Tip angle of wings, 10°..
53 Position of wings
54 How guyed
55 5.

57
58 Position of tail
59 Angle of tail, 7° 30’......-.-..cece cree e sees nett cert ecto eeee
60 Co-efficient elasticity of tail, 1240 grammes at center to

deflect it to the horizontal... =
a Position of rudder
63 Line of thrust, 1500
64 Center of gravity; of whole.
65 Center of gravity
66 Center of pressure; of whole estimate.
67 Center of pressures

11,248

54

20
tor

cK

26.3

ee A ei nail el — 9) a a
*
APPENDIX 301
DATA SHEET No. 5.
Weight of Aerodrome No. 6, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, June 22, 1899.
Parts. Sizes. | Weight. ees ;
Metres. | Feet, aa aes

Front end of bowsprit, 1685.7.

Back edge of cylindrical part of
float, 1606.5.

Front end of midrod, 1613.7.
Front edge of F. W., 1595.7.

te

C. of P. on F. W., 1563.
Back edge of F. W., 1515.7.

Line through center of propellers,
1500,

C. of G., 1484.4.

Front edge R. W., 1406.5.
GC. of P. on R. W., 1374.5.
End of midrod, 1351.8.
Front end of rudder, 1335.
Back edge R. W., 1826.5.

Center of rudder, 1279.5.

Back end of rudder, 1221.

Rey. x diam. x pitch ratio x thrust

*H. P. =

+ This is calculated on the assumption that the center of pressure on each w
2-5 the way from front to rear,
and that the tail proper bears no part o

minute is in ordinary curved wings
efficiency per surface of the front ones an
this efficiency is smaller or larger per unit of surface.

33000

that for wings o' 4 :
f the weight; but if rear wing is smaller or

ing or on pair of wings at a motion of 2000 feet per
f usual size the rear wings have 2-3 of the

larger

302 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

DATA SHEBT No. 6.
Weight of Aerodrome No. 5, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, June 23, 1899.

Parts. Sizes. Weight. Remarks.

Metres, Feet, Gromaae| Pounds.

= soe

1 Frame, including everything of metal, permanent and | ~ Front end of midrod, 1611.5.
undetachable, such as bed-plate, cross-rods for the
support of propellers, bearing points for clutch, ete...... Rabe cadn|boocasac 8050
2 Engine Be ca : 464 Front edge of F. W., 1609.7.
3 Pump, $34; pump shaft, 55. 389 4
4 Hull covering ....-......... 398 .
§ Gasoline tanks, air tanks, valves, ete ne B48 C. of P. on F. W., 1577.7.
Gismokestacks pesimeeceeeeieoeccle re soopedonbas be 373
7 Float, 275; drop piece for rudder, odode 360
8 Reel, 128; steam gauge, 81....... Beescceaccage : 209 Back edge of F. W., 1529.7.
9 Wing clamps, 200; guy-post clamp: a6 232
10 Boiler, 764; burner, 170; counter, § 1029 .
1] Rear extension to midrod................ 174 Line through center of propellers,
12 Separator and pipes to engine and pump 602 1500.
13) Exhaust (piped aae- cso cece acacmecemices ot
14 Front lower bearing point, 84; clutch post, 41 onllo 20 126
15 Rear bearing points, 146; extra strengtheners, 32..........]..+«..-- “poacoce 178 C. of G., 1494.6.
UG} anobaacdhcoAgsobapanconesas
17 Wings (without clamp) mafereo| (otareele obS 2342 es
18 Tail (without clamp).. Front edge of R. W., 1411.7.
UNINC ane staseoges 322
20 Guy sticks, each 56 112
Pali sya) conacoumeeoacooneccor 837 C. of P. on R. W., 1879.7.
22 Extra length of midrod at front. 129
23 Wood bowsprit .-.:.-:-.:.2..... bu .
Other things ... 1 Rear end of midrod, 1360.3. |
Spaced iiactnds: S| Rae, |kaseaaoo. |) ate) Rear end of R, W., 1331.7.
ooaoo00 ae 1400
-
Ssaboo0 wee eel) 13,079 i]
= wee q
38 Tota] area of support (not including tail)........... Beats rears 68
39 Tota) area of support in feet, divided by total flying A q
rei bein el ba ween ee : t
Total area of horizontal tail. 6.94
Total area of rudder (vertical)...........ccecsceseees E 7.64
2 Horse-power at brake.... Horse-power by formula *...... a
OUI On i enneC ee eccocnicnnnrinrinn trinity }
Lift at pendulum (during one minute absolute).......
Lift at pendulum (during one minute in terms of wt.) |
Minimum pressure with which wheels turn..
Position of center of pressure of wings 7..
Root angle of wings, 10°
52 Tip angle of wings, 10°.

Position of win
How guyed

58 Position of tai
9 Angle of tail,

Line of thrust,
Center of gravity, of whole
biCenter of igravitya..1. csc seceaasenen

66 Center of pressure; of whole estimate.

67 Center of pressures............eec00ee
OSie ome cerisn

69 ...
th) 500
Le ate

mp
72

Rey. x diam. x pitch ratio x thrust
33000

+ This is caloulated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per
minute is in ordinary curved wings 2-5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
efficiency per surface of the front ones and that the tail proper bears no part of the weight; but if rear wing is smaller or larger
this efficiency is smaller or larger per unit of surface. a

*H. P. =

APPENDIX 303

DATA SHEET No. 7.
Weight of Aerodrome No. 5, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, July 12, 1899.

Parts. Sizes. Weight. Remarks.

a “ne Metres. Feet, Grammer) Pounds,
1 Frame, including everything of metal, permanent and | Front. aa =
undetachable, such as bed-plate, cross-rods for the Bost SO CEO Went a ZU se
support of propellers, bearing points for gears, clutch,
4 IBIS, (BiG, “geoponndan soobesuosqusAd 8050 Front end of midrod, 1611.5.
OA Shy SIRS“ sas onaoponcedoonpedberdbonbouOOoboDaDOOOnNS 464
3 Pump, 334; pump shaft, with § 2
SNC VOR oe Dose cwataas clcicci elas

4 Wull covering, 2

889 Front edge of F. W., 1609.7.

: g d separator, 398
5 Gasoline and air tanks, 167, 165; air valve, 16 S48
6 Smokestack, 310; piece to protect midrod, 63..... 373 C. of P. on F. W., 1577.7.
7 Float, 275; drop piece for rudder, 57; guy-post, 18. 350 ,
8 Reel, fork and float, 128; steam gauge with pipe, 81 Slloar Re 209
9 Wing clamps, 200; guy-post clamps, 382......... era loree aes 232 Rear edge of F’. W., 1529.7.
10 Boiler, 764; burner, 170; counter, 9. 1029
11 Rear extension to midrod.................. 174
12 Separator and pipes to engine and pump. 502 Line through center of propellers,
16} Losey joys RE os opaoeacqou dds soudeoddodcn 84 1500,
. 14 Front lower bearing point, 84; clutch post, 41... 125
15 Rear bearing points, 146; extra strengtheners, 32. Ae 178 .
1G saqoobodpp ands COSC aHaCH ACHE REHA cea ba eoeeraeenae i Front edge of R. W., 1411.7.
17 Wings (without clamp) (2180 in 1896)...........-cececereclescecces cae cele 2342
18 Tail (without clamp}; part of rudder... 2
19 Rudder reduced (No. 2 or new one, 299) cial efeseretctrtstel| aencersvebeiols 822 C. of P. on R. W., 1379.7.
PONG Miya Sbicks sy Cache 56. ceric ccc vie nie's [ciclo cis eeteisicinle clerniots 112
21 Propellers (95 cms.; wood, §37; 95 cms. canvas, 548) 837
22 Rxtra length of midrod (front), 129............. 129 End of midrod, 1360.5.
23 Wood bowsprit (complete), 132.... 3 132
2a Other: things! scn cece sec ss
25 .. 3asc Front end of rudder, 1343.3.
2G) erie 9
horleagnbabseocoaaabae Solloaes. nad} Goadana 200
3 BY Ne ar Bs , 1400 Back edge of R. W., 1331.7.
Center of rudder, 1288.
|
al ena fh cidtajetnie\ Lye) Back end of rudder, 1229.5.
35
BYe sonra oe
38 Total cluding 68
89 Total area of support in feet, 3
rele hterinel Dsante sien eiclayactan ciaalsiniciatelsleatclsin’s cieleleleicinrs
40 Total area of horizontal tail... 6.94
41 Total area of rudder (vertieai)... - -8q. 7.64
7A Horse-power at brake.... Horse-power by formula *...... |
ASP eneee re eter inctecicns tinamarislanie asics slsseelecismiciviss 7

44 Lift at pendulum (during one minute absolute)
45 Lift at pendulum (during one minute in terms of wt.).
46 Minimum pressure with which wheels turn..........

47 Position of center of pressure of wings 7....

51 Root angle of wings, 10°..
52 Tip angle of wings, 10°.
58 Position of wings.......
54 How guyed

58 Position of tail.
59 Angle of tail, 7° 30’... 2... csecerecencercesecncesrsescescnes
60 Co-efficient elasticity of tail, 1240 grammes at center of

rudder to bring it- to a horizontal; 490 grammes at

point same distance from front end of rudder as length

of rudder of 1896, to bring to horizontal.............+++.
GEsPosibiony OfsTUGO ease cieciscis nis sietar aes aletaslale bd
(Gr) SRonanE DODD EeODOOSODSO
63 Line of thrust, 1500.........
64 Center of gravity, of whole
65 Center of pravitye.. 2.5.2.5 sce eseces
66 Center of pressure; of whole estimate.
67 Center of pressures.... eens

Rev. x diam. x pitch ratio x thrust
33000

+ This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per

3 ea : A 9.5 i é iz ying: ye 2-8 of the
minute is in ordinary curved wings 2-5 the way from front to rear, that for wings of usual size the rear wings have 2.
efficiency per surface of the front ones and that the tail proper bears no part of the weight; but if rear wing is smaller or larger

this efficiency is smaller or larger per unit of surface.

*H. P. =

304

DATA SHEET No. 8.

Weight of Aerodrome No. 5, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, July 19, 1899. —

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE

Parts. Sizes. Weight.
Metres, Feet, |Grammes.| Pounds,
1 Frame, including everything of metal, permanent and
undetachable, such as bed-plate, cross-rods for the 2
support of propellers, bearing points for clutch, etc...... 6 3556
2 Engine, gears, shafts, ete. 476
3 Pump, pump shaft........ neieteta B89
4 Hull covering, 264; apron, 1 piece behind separ: 398
5 Gasoline and air tanks, 167, 165; air valve, 16. B48,
6 Smokestack, 310; piece to protect midrod, 63. 373
7 Float, 275; drop piece for rudder, 57; guy-post, 18 350
8 Reel, fork and float, 128; steam gauge with pipe, 81 209
9 Wing clamps, 200; guy-post clamps, 32............. 232
Boiler, 800; burner, 170; counter, 95 1065
Rear extension to midrod............... 174
2 Separator and pipes to engine and pump. 502
Wxhaust pipe J. hacc% a cics vice manisiee stoma melee 84
Front lower bearing point, 84; clutch post, 41. 125
Rear bearing points, 146; extra strengtheners, 32 178
Wings (without clamp)............. nA 2446
Tail (without clamp), part of rudder
iMG soconugdeosboceagososmnt coe 299
Guy sticks, each 56.... 112
Propellers, 95 em. wood.. 837
2 Extra length of midrod 168
3 Wood bowsprit 78
Other things
200
1400

Total area of support (not including tail)..
Total area of support in feet, divided by

Total area of rudder (vertical)
Horse-power at brake.... s
Lift at pendulum (during one minute absolute)....
Lift at pendulum (during one minute in terms of wt.).

Minimum pressure with which wheels turn
Position of center of pressure of wings 7.

Curvature of win
Root angle of wings, 10
Tip angle of wings, 10°
Position of wings.
How guyed

Position of ta
Angletotitalls Gteentienssciee ieee rsee
Co-efficient elasticity of tail, 200 grammes at cen’
deflection to horizontal.
Position of rudder........
Elasticity caused by two ¥%
two 14-inch bands, in tandem, below
TinesoLihrustydod0s. cece ose: ose
Center of gravity, of whole.
Center of gravitys...........
Center of pressure; of whole
Center of pressures

6

62

$-inch rubber bands above and

ter

*H. P. =

Rev. x diam. x pitch ratio x thrust

33000

Remarks.

Front end of bowsprit, 1683.5.
C. of float, 1614.5.

Front end of midrod, 1611.5.
C. of reel and float, 1577.5.

Front edge of F. W., 1609.7.

C. of P. on F. W., 1577.7.
Rear edge of F. W., 1529.7.

Line through center of propellers,
1500.

C. of G., 1498.

Front edge of R. W., 1406.7.
C. of P. on R. W., 1874.7.
End of midrod, 1360.3.
Front end of rudder, 1343.5,
Back edge of R. W., 1326.7.
Center of rudder, 1288.
Back end of rudder, 1229.5,

N. B.—Distance between C, P. on
F. W., and C. G. = 79.7. Dis-
tance between C. P. on R. W.
and C. G. = 123.3. If the mean
C. P. is to be over the C. G. we
should require an efficiency for
the rear wings of 64.6 %,

__t This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per
minute is in ordinary curyed wings 2-5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
efficiency per surface of the front ones and that the tail proper bears no part of the weight; but if rear wing is smaller or larger

this efficiency is smaller or larger per unit of surface.

ae Me li li se wt Mt Me tie tee si a i ie

SB Adie, bel

———— ee

no. 3 APPENDIX

DATA SHEET No. 9.
Weight of Aerodrome No. 6, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, July 27, 1899.

308

| Remarks.

Front end of bowsprit, 1695.7-
Front end of midrod, 1623.7.
C. of float, 1618.2.

Reel and float, 1576.7.
Front edge F. W., 1595.8.

C. of P. on F. W., 1563.8.
Rear edge F. W., 1515.8.

Line through center of propellers,

C. of G., 1485.5.
Front edge of R. W., 1406.7.
C. of P. on R. W., 1874.7.

End of midrod, 1352.2.

Parts. Sizes. Weight.
|
Metres. Feet. |Grammes,| Pounds,
1 Frame, including everything of metal, permanent and
undetachable, such as bed-plate, cross-rods for the
support of propellers, bearing points for clutch, ete. iyd
2 Engine, gears, shafts, etc......c..c.eccee0s ; ea
3 Pump, 123; pump shaft, 49 oe 172
4 Hull covering, including apron and piece behind separator.|..- 274
5 Gasoline and air tanks, 167, 174; air valve, 18 ane 361
6 Smokestack, 319; counter, 95; burner, 170.. 54
7 Float 290
8 Reel, fork and float.. 128
9 Wing clamps, 188; guy-post clamps, 24..... 212
10 Boiler, 764; steam gauge and connections, 7§ 843
11 Front bearing point, 75; clutch post, 58; r
ip intoswtoamencie ssnissaaseiesine ecicclon eelatineeac ease ell eee 288
12 Separator and pipes leading to engine and pump. Aokcaga iad 2
ag Drop piece and guy-post for rudder............... 51 Ganaoscs 76
CY oe segeo Minialeincaidielerstelstsietsiatelei<ta1clateiwielare)
15
iG} Ye AC
MAINS RRwichouts clamp). repaired vee ssanceticeee ons sok tnen mal cesoeeeallccesene 2128
18 Tail (without clamp).........
DO Rudder Series tclemts stents 299
20 Guy sticks . 406 1500.
21 Propellers ...... 628
22 Extra length of m 877
23 Wood bowsprit 8
ee Other things (canvas keel, 36; rudder, 76). 112
Ma. sod ao seequaconcUeedosOnnee
PrPMUelE Ca EgStAnlin Petlip Nt) epictest ooecin celeecat ater ieestciee ee ctestelonemece beck sees 175
SOMWALCLM (AL SLALARE IPTG) sta cicaie ate sinters ctewic ieiniet ciaeicing cee na | eeeanne | aac 1525
o}|oe0d asee elsicfeame se OlG

38 Total area of support (not including tail)........... Betta occene
39 Total area of support in feet, divided by total flying
eI taa Deer elerleielsre ciersicicia sincerest scie ctevcieialow sinisteim eters cite

40 Total area of horizontal tail..
41 Total area of rudder (vertical)
42 Horse-power at brake.... Horse-power by formula *
43

44 Lift at pendulum (during one minute absolute)...
45 Lift at pendulum (during one minute in terms of wt.
46 Minimum pressure with which wheels turn...........
47 Position of center of pressure of wings f:....

50 Curvature of wings, 1 in 18
51 Root angle of wings, 10°...
52 Tip angle of wings, 10°..
53 Position of wings........
54 How guyed

58 Pos’ of tail..

59 Angle of tail, 5°.

60 Co-efficient elasticity of tail,
deflect it to the horizontalic 7... 00.5. ccc cw ccs en cncnee

61 Position of rudder..........

62

64 Center of gravity; of whole..
Gb Center of pravitys.. 2.0. .0. ccs. rcescene
66 Center of pressure, of whole estimate.
67 Center of pressures

415
ain

Front end of rudder, 1333.9.

Rear edge of R. W., 1326.7.

Center of rudder, 1280.6.

Back end of rudder, 1219.9.

*H. P. =

Rev. x diam. x pitch ratio x thrust
33000

+ This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per
minute is in ordinary curved wings 2-5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
ficiency per surface of the front ones and that the tail proper bears no part of the weight; but if rear wing is smaller or larger

this efficiency is smaller or larger per unit of surface.

34

306 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27

DATA SHEET No. 10.
Weight of Aerodrome No. 5, Flat Wings and Pénaud Rudder.
Certified to by Chas. M. Manly, July 27, 1899.

Parts. Sizes. Weight. Remarks.

Gram mien Pounds.

Metres. Feet.
1 Frame, including everything of metal, permanent and 13 grammes of lead on end of
undetachable, such as bed-plate, cross-rods for the bowsprit.
support of propellers, gears, shafts, ete. (such as guy-
wires and turn buckles, 26g). Ae Raiteicteien'||) OBS ;
% Engine 2.22 cscs ces oes 0 venenne amacsleslaenwan ete 6 476 End of bowsprit, 1708.
3 Pump, 301; pump shaft, 55; support to pump, 33... oe eee 389
4 Hull covering: front, 47; sides, 92; top, 46; small side
pieces, 44 229 C. of float, 1622.
5 Gasoline and air tanks, 167, =,
80; piece rear of separator 20.... 400 d
6 Smokestack, 310; piece to protect mi 373 Front end of midrod, 1619.
7 Float, 290; drop piece for rudder, 57 B47
§ Reel, fork and float, 128; counter, 95 223
9 Wing clamps, 202; guy-post clamps, 33 2385 Reel and float, 1601.5.
10 Burner, 170; boiler, 759......-..- 929
11 Separator with tubes brazed to it............+- 615
72 Steam pipe, 87; steam gauge and connections, S1...... 168 Front edge of F. W., 1609.7.
‘xhaust pipe, 90; wooden plugs in nose of frame, 10.. 100
14 Upper front bearing point and clutch post.........--..--- 136
15 Lower front bearing point, 84; lower rear bearing point, G. of P. on PF. W., 1577.7.
145; clutch, 41 Px
D6) ociceciecie nleisieoee.eeeleninsnelinnale
17 Wings (without clamp), front, 2 x 2534 Rear edge of F. W., 1529.7.
18 Tail (without clamp)
19 Rudder a 299 F
20 Guy sticks, front, 65; rear, 50.. E 114 Line through center of propellers,
91 Propellers, 100 em. round ends, 30° blade... ; 757 1500.
92 Extra length of midrod, front, 174; rear, 22 De ot
293 Wood bowsprit (heavy ONne).........-. cere e rece ee cere ecees lores tes
9 Other things! 2.-:2s------s ee C. of G., 1498.
25°: A
97 Fuel (39) at s « as Bt ies et ee |e eo 99! Front edge of R. W., 1404.7.
98 Water (2000 at starting fligh Ne 1500
id on bowsprit to balance eae 13 C. of P. on R. W., 1872.7.
31 Sundries unknown ....... bas
Bor isinia dinlnverstalelalaletale ele ae < a
33 pEchacoRo a aesnsp gts End of midrod, 1350.3.
Re Bie Seesteretall enieme ey (eles COk 1 03
36 3 Front end of rudder, 1333.5.
37 BOA Re RS DHACOOURRECocL HO USenCOLononacuMDnyededonaece.
38 al area of support (not including tail)........... SQeilbe| cele | OS
39 Total area of support in feet, divided by total flying Back edge of R. W., 1324.7.
wesiy Tra a coe mise tatoc lacie leralcle lolol wuiicteicleweiciereinialermipieteteiel= 2.195)
40 Total area of horizontal tail.. F 6.94
41 Total area of rudder (vertical)..........2--e-ee+2-+- 7.64 Centre of rudder, 1279.5,

42 Horse-power at brake.... Horse-power by formula *

44 Lift at pendulum (during one minute absolute)....... Mears end) of rudder, j 1222.

45 vu at pendulum (during one minute in terms of wt.)

46 Minimum pressure with which wheels tum......-.... .

47 Position of cente Ore ie Distance between C. P. on F. W.
a cra ion of center of pressure of wings 7.. and C. G., = 79.7. Distance

between C. P. on R. W., and C.
G. = 125.3. If the mean C. P.
is to be over the C. G. we
should require an efficiency of
63.6 for the rear wings.

&) Curvaty
V1 NOW 2 cncccenecceccctercecsvercccercsvevesecvcserss ob
51 Root angle of wings, 10°..
52 Tip angle of wings, 10°...
53 Position of wings....
54 How guyed
iy aceon sia\aia
56 ..
iO asgabaeoccpcassod
58 Position of tail... .....-. 2. ccc eet e none
59 Angle of tail, 5° elevation at rear end........---.-.--.-++--
60 Co-efficient elasticity of tail, 200 grammes at center to
deflect it to a horizontal
61 Position of rudder
Ory a -patoagsanoo 30
63 Line of thrus OO Sersrciisicaice stare
64 Center of gravity; of whole, 1498.
65) Center of pravitya. ons .ce eee cece isles
66 Center of pressure, of whole estimate. .
67 Center of pressureég..........
68 ..
69

Rey. x diam. x pitch ratio x thrust
33000

_ + This is caleulated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per
minute is in ordinary curved wings 2-5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
efficiency per surface of the front ones and that the tail proper bears no part of the weight: but if rear wing is smaller or larger
this efficiency is smaller or larger per unit of surface.

*H. P. =

no. 3 AP

PEN DIX

DATA SHEET No. 11.
Weight of Aerodrome No. 5, Superposed Wings and Pénaud Rudder.

Certified to by Chas. M. Manly, August 3, 1899.

307

Parts.

Sizes.

1 Frame, including everything of metal, permanent and
undetachable, such as bed-plate, cross-rods for the
support of propellers, bearing points for clutch, etc......

2 Engine, complete ........

3 Pump, 301; pump shaft, 55; support to pump, 33...

4 Hull covering, 276; apron, 117; piece behind separator....|...

5 Gasoline and air tanks, 167, 165; air valve, 17

6 Smokestack and piece to protect midrod................ a eee

7 Float, 290; drop piece for rudder, 57; guy-post and
CLETINEY WL dpreste terete aletste'elnielessiets e'sisteisielstsialsicte wintelaisietetsisicieisiersiep= ere
8 Reel, fork and float, 128; steam gauge with pipe, 81.
9 Wing clamps, 202; guy-post clamps, 33
10 Boiler, 775; burner, 171; counter, 100.
11 Rear extension to midrod..............-
12 Separator and pipes to engine and pump.
TR DA ElH Tyre GeSoopeanaocdodososcosppe dsoncoone
14 Front lower bearing points, 84; clutch post, 41
a Rear bearing points, 146; extra strengtheners,
17 Wings (without clamp)...........
18 Tail (without clamp), part of rudder.
TOUR VG r ee tateiniaistslelelclais ee /s)elvicieiaiesiersine
20 Guy sticks, each 60...
21 Propellers, 100 cm. round end.
22 Extra length of midrod, front.
PAV OOCMDO MS DLL ls ete ate ccteleistetelelsivlota\eleisls aisle sieicinieltelat ale
24 Other things, 248 grammes of lead on end of bowsprit

27 Fuel (at starting flight)...
eS Water (at starting flight)
SC) Brrxinto'afala'einte(n’ viel aie sivt=
31 Sundries unknown .
82)...
33

38 Total area of support (not including tail)........... sq. ft.
89 Total area of support in feet, divided by total flying
WOlE ised (LOS \elelsewinlele piciveinis.e isle

40 Total area of horizontal tail..
41 Total area of rudder (vertical).... G
a Horse-power at brake. Horse-power by formula *......
44 Lift at pendulum (during one minute absolute).......
45 Lift at pendulum (during one minute in terms of wt.)
46 Minimum pressure with which wheels turn...........
47 Position of center of pressure of wings f....

51 Root angle of wings, 10°..
52 Tip angle of wings, 10°..
58 Position of wings..

56

57 ...

58 Position of tail.. :

59 Angle of tail..........ccec sence scene eee teen eee en crete Sesiese

60 Co-efficient elasticity of tail, 200 grammes at center gives
deflection of 5°...... eretelataisterbistainieietelota olelalerolaiste aa sigieieinlelaleie’e.

61 Position of rudder...........-.--.-

62 Elasticity caused by rubber bands.

63 Line of thrust, 1500...........++6+

64 Center of gravity, of whole.

65 Center of gravitye........-..6-

66 Center of pressure; of whole es

67 Center of pressurés......--+.eeeeeeee

Weight.

| Paonia Pounds. |

14,364

Rey. x diam. x pitch ratio x thrust

*H. P. =

minute is in ordinary curved wings 2-5 the way from front to

efficiency per surface of the front ones and that the tail proper bears no part of the weight;

this efficiency is smaller or larger per unit of surface.

33000

Remarks.

C. PR. on FP. We, 677.7.

Line through center of propellers,
1500,

C. of G., 1498.

C. P. on R. W., 1872.7.

+ This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per

rear, that for wings of usual size the rear wings have 2-3 of the

but if rear wing is smaller or larger

308 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE vou. 27

DATA SHEET No. 12.
Weight of Aerodrome, One-Quarter Model.
Certified to by Chas. M. Manly, June 11, 1901.

Parts. Sizes. Weight. Remarks.
Metres. Feet. poet Pounds,
1 Frame, including everything of metal, permanent and
undetachable, such as bed-plate, cross-rods for the
support of propellers, bearing points for clutch, etc..... sens B245
2 Engine, bed plates and sparkers eeieieteleie a 4549 10
3 Gears, shafts, etc.. ono) loqosmono 1662
hae
ie
6. piatete ate iatota 55
7 Floats, front, 212; rear, 22 432
Si Reels) float and icords sill syne tcepciciae certs al seiaictteels 142
9 Wing clamps, 26 and 97; rudder clamp and post. 183
AOU CarDUT chor Rano MnCl awerettaaleliataestciecieilteeataiteatter opaddllon 137
11 Spark coil, 1512; holders Be alasyal| ete 1622 |
PARA Cons Eondeescornacoooundesnos aaecons 1627
18 Primary connections
14 Secondary connections .
15 Guy-post clamps, each 13 in} ve'al al] haretevotete ie 26
16 heme ate
17 Wings (without clamp), new flat wings. na 2ASt
18 Tail (withcut clamp), Pénaud rudder. 353
19 Rudder, wind yane..........02...22+ 88
20 Guy ‘sticks .2...00...5 odvocas 30
21 Propellers, 585 each.............. Oba0 1170
22 Extra length of midrod, front, 125; creediy.
23 Wood bowsprit <................ < BoSUnccel saan eens 75
24 Other things ..
SL COMME Tat aletciercistciciceaintainiciemsiciemietseietetele sae 110
Guy-post clamp and post for rudder. anes 16
PIO SOuD OCD 53
. 19,104

88 Total area of support (not including tail)........... RGB) asonood 61.41
39 Total area of support in feet, divided by total flying
weightpin#lbs:.sscccee cote. Geet aeene 5 1.46

40 Total area of horizontal tail.
41 Total area of rudder (vertical spas
42 Horse-power at brake 1.5 at 750 R. P. M.......

43 Engine gave 2.01 H. P. on brake at 900 R. P. M.
44 Lift at pendulum (during one minute absolute).......-
45 Lift at pendulum (during one minute in terms of wt.)....
46 Minimum pressure with which wheels turn................
47 Position of center of pressure of wings 7...

Curvature of wings, 1 in 2016
Root angle of wings, 10°..
52 Tip angle of wings, 10°...
53 Position of wings: C.
1386.9 ....
54 How guyed
55 Position of ta

56 Angle of tail, [Ne ORR St sere ere islole miele elererorcvelmieiaie tolerate
57 Co-efficient elasticity of tail, 200 at center depresses to

horizontal! eesti seicie'emciiesecianidesicre isan matte bie ete ae iee rae
58 Position of rudder (center), 1292.9...
DO Ee cheiain cininisialalsinialecarstt nieiriatcicloraiselseicte Mette hteree cece nia
60 Line of thrust, 1500, through center of propellers...
61 Center of gravity; of whole, 1503.7...........+++-
62 Center of gravitys, 2497.5.............0%
63 Center of pressure; of whole estimate, 1503
64 Center of pressures, 2513 a5
65 Center of clutch post,
66 Center of coil, 155%
67 Center front float, 16.45.
68 Center rear float, 1872.6........
69 Center wind vane rudder, 1435.6
70 Center Pénaud rudder, 1292.9..
71 Rear end Pénaud rudder, 1215.9
72 Front end of bowsprit, 1707.2

Rev. x diam. x pitch ratio x thrust
32000

_ 1 This is calculated on the assumption that the center of pressure on each wing or on pair of wings at a motion of 2000 feet per
minute is in ordinary curved wings 2-5 the way from front to rear, that for wings of usual size the rear wings have 2-3 of the
efficiency per surface of the front ones and that the tail proper bears no part of the weight; but if rear wing is smaller or larger
this efficiency is smaller or larger per unit of surface.

*H. P. =

Aerodromics, science Of .........cccc ese ccc cece erence recat et eces ener ere cceesssserccscsecees i

INDEX -

A
PAGE
Abbreviations and symbols for points on aerodrome ...........e.ececcecececeecececceceecses 14, 15
Accidents, in launching large aerodrome.......-.......0c.--cecceececscceee, 126, 184, 185 265-281
Lossmotemod elyaerodrom crm rmeyacise eee eee aimee eee be ck 1 7, 94, 154
AGTTNTIEE) ENG GT it) ie Aca Cee SORE Se ears ey oe Gk adie Ey rn el. 55, 56, 59, 60, 65, 66, 112
AcKiaAlnavization, meport of Board of Ordnance One sas cees soa. seen een one oe ncien ene 276, 279
Aerodrome, DVLA CINE OLA ye fateh che ere cs or on 45-52, 81, 90, 109, 134, 211, 212
CONSULUCHLONW Of 2), stanterns asin ele cle Re ee ne eee ee 53-80, 164-187, 234-250
definition ofswond! ngs sna e eye peers ete aera Er hale AR ey te iii
dimensions of (see aerodrome models and data sheets).
elehth:eizer model: 5 vance. cece easel ease ee EEE ee 133, 134, 154
engines (see engines and motors).
experiinentss witht MOdelS).\:cccvac eaters sien co aclea eee aie ieee ce 6-14, 16-24, 133-155
field trials (see trials).
HTS Lite htiotemod els Mavi bse S96 ace rece eisemicte cidtoinn meen oon eee By os LOT, LOSS TL
Arstwtrialotea. ihyvinewmMachinel sau) ree. alr): is se eeeiseeeaecieie ecient 97
flight (see also trials).
ANS Model, w May. USOC. a. ceteris = cress eisia are ctor sieus ers (o. nrsloals lala Seevarsterate Baron LO ue
larezeymachine (A903) 1. <inacoys <erciec atc onto e since epee aiste sets 126, 127, 255-282
DH OLOLTADHS OL srec.corsctevets ccs crocs see ib, Hee eee ove eine Peeler eaters 108, 259, 260
NEAT EO Mirye set cteneys eae sya etece ace ai hey Ss ied ova dane a okey eM 126, 127, 129, 130, 156, 183, 225, 255-282
CON SERUCULON OL faccityct to cccceieiciay e1ciere Syeccpeheleteke eset choke leucine eeToe trate 164-187, 234-250
latnchings apparatus: LOVa i. -c1-,spsjcic eyes) fo creve cisve = s.<tcisva/<)e/efeiciele eet = eates Sime 156-163, 183
SHO EOSLS rst rat eke ci aey os aces ons ois sy eie etats tovss arated fw tle hanes lana Grain eats helt Peyaietoteras arate tenetaye lee 251-254
MTDC CLO Ooi) i ayatrsta:ctaceve peters cee ns os suebal ey eheoe eer oe vets payne orate elie leesreieh a aka mete ea iereee 126, 181, 255-282
SW GL SEN OSs tcyesckevarct anc cgavetecsreieyese w:olasb avec sio:e anesataue ais bv raters al eis mie olen ah atarsliaverafetshopsaers terete oust 277
launching apparatus) LOK MOGeISs es nclcteresyeiel esi ers fre eee eile 92-122, 133, 134
large: Aerodrome’ af .5 scsi heirs teens ainietetete sietecoin aks 156-163, 183
man-carrying (see also aerodrome iarge) .. 123, 125, 129, 130, 151, 153, 156-187, 234-250,
2bbs aoe
model, descriptions of (see also data sheets).
NOP ae 4 Seroeoreicdadsoainea cot 21, 30, 31, 36, 38, 40, 53, 55, 75
NC att |e A ee eS Pa Cr ainaeorin gee 28, 29, 38, 40, 53
IN 0514 che srs, srereceucie, 53, 62-67, 69, 70, 72, 75-79, 81-83, 86, 92-109, 120
NOM beer tetene 26, 64-66, 69, 70, 75-79, 81, 82-84, 86, 88, 89, 90,

92-109, 110-122, 130, 131, 134, 135-155, 158, 174,
188, 189, 208-210, 231, 257, 281.

INOILG 02 1tct coe stare ele 49, 61, 62, 78-81, 89, 90, 92-109, 110-122, 130,
131, 134, 158, 174, 188, 193, 208, 210, 231, 257,

281.
PUD DEL-DUL so aieievaccyate ciclotevehel statst cVercturs ocelotave sol svalotatal shale ieLale\nl lefeintere 11-20
CLETNED-SIZOl Seal oyns crore: sooo © eralaie fetistereke let's) apey=i sales o Tato ier abel ste oieloher tal apseieleiats 138, 134, 154
HeNTY SOM RAO Uridine Go onor EOaeee OOdho OSC OCU Ot 39, 53-80, 90, 112, 119, 129
AUN CHINE Ap PALACUS LOM cetera ta eievale elettale rata eco) alelna se eteielolele clots (etetwislelers 92-112, 134
Qularter-sizeg yatta ori otiere ieee tienes 158, 159, 170, 226-233, 234, 255, 257-261, 281
TESULES LL OWN apo re hae one e te creek Ce kayet ora alncahs sa popa sala’ intel n (ols iellelslnpejeielanelvinjeiatere)einie) 17, 129
steam driven (see also Nos. 5, 6). «20. ccc cle e cer cacecccens 122, 164, 165, 224, 281
ENIAISS OL SINOSS Gi Ly poet (WLS O ea) pMajaneis excratcraieys ei-iatehaisicinjeiate alele eis rip mle loteie eialnlels 29, 53
INOS Oe GES OG) evrevercrePeraie rel slelotc t= rel eb eleinlietata letatators) <loyetalstals otxtels 63, 92-106
INOS Ss 5 4Gis LS OG hevarstavcte rotate rales (ol ieveiseye ele cle weslete ett slapetemnsavelCiohens 2, 79, 106-109
INGOT CLS OSI scree wea ateretosaklers eeteysleeletesobefaies eis vfotszavaln afar = yates lates /at= ist =lelaibh< 61
DOS Gt (99) rer totate sro lcacrete toc sie wteicte letersi ste aiertere 49, 79, 135-155, 231, 257
INOS!) 302031 samd OUNETS! fie)< om - o ereeieisieie a cl= anise wie 0, =!e'w ale wiels 6-14, 17, 19

motors (see engines and motors).

quarter-size models (see aerodrome models).

rubber-power models ........--eecce eects ere eee e terete teeters eee eeeeee tees
weights of (see weight and data sheets).

310 INDEX vou. 27

PAGE
A CLOCYMAMICE: sieve ic clale oieialteeloteretateloierale o/alstaleta lara tetelstaralo)neletaloietets lateleloteteiatey sitaps 7, 30, 43, 44, 80, 91, 99
Experiments in Were cr. ehelscieicteeiciorteipete erate 1, 6, 7, 19, 21, 32, 41, 80, 98, 128, 150, 153
* Aeronaut (see “Gls0/ aviator) oc. sec cass coe ce le aide lee acters eis ers etc oleate ate ince 130
AAT; (COMIPTESSEG! = sere aleve arc fevoteisicucne as lelertalcteiete cedars tetova arene statetsmentctntaltat= eile eater ets 11, 24, 25, 26, 68, 112
VR QTC reo ow casei hesciers oteiela ores otot ale intanstelspelahe betescecis © ctatetalel stetenet aerate rietetetneet stats stata tee ete ee 154
TOSISCAICE OL 2S sieicce Sis. cls'e cieis. gs elalcge ofa yale oyoistans tecnednye eth aiateteiavatottaielatciavatarnaiatalots 6, 8, 9, 142, 165-167
Air-chamDer.-2tikepceievee-win hace stereo loveve tere ass cyereie ote teic ratte ota te teeta Reacite Per cenicovatet te sk arainctaie 64, 68, 69, 98, 112, 113
Air-cooled. CNZINE: oc oo sc)s cate -atove wise wpers ois loveteto tel ole love ote lepatele ever sreseterare atone taieiatefntal chekelnVereke feta fears et aera 226
Alcohol and hydrocarbons, useofasiituelic- eee eran ine eerie 24, 25, 35, 5b, 57, 66, 72) Ts
Alcolol-‘acolipiles "5. sn, chet srienise ene cle ire eee tick Eee EE Cieiketeriatart 55, 56, 60, 66, 69, 112
Allegheny. Observatory, experiments ate a -alerer-rleiecletets cbalelebelteliobeleletelebeleist sete leteliaSeleletetel stats allele ash a ei)
Allotment, Government, for man-carrying aerodrome ...............+-seesseeeees 124-126, 132, 278
ATuminum-bronzer USO OL- <crrreriecclere niaicle cleis clot cee ke lotta elelevetetete eteketeksteletete istet stellata t= relate a= 114, 116, 173, 174
Aluminum: in engine COBStuCtLom te << ie ie velel=teleteketatesteleerelel ele eteie ie ehaiteatel siete ete tetas 32, 114, 243, 252
sheathing: of- Rul]. = 5% /.ceraye so sicete os ererels elaine elcrolcke ice reelaistote totale tole tavone Yate ie tatetera tale iean 69
WATS Seo sicia sed revdy ave sus ia: aye ate rauate sein © otorer svete ate Cre oath Latino te shen eae hs eke taka notokotets is Rebs trart=t 84
Aneroid barometer for determinine) heist. qsrs r-rel <tereicreteleteletercielaietetseks elsiarecheteciahe ale ere ie ien tele yete 186
ANEMVOMECECK. CUPS). ois siercre.cielejetece sey eleteVols yo ois y=sretels usioheneverekele’a stele tel cami etobeboiol cpenersteh tee (tenets fotstetsueiaaeetatstats 143
Angle) diedrall sof: WANES. «ar «Kel orelerstelsreta ode elec tore ole Repeats otelene eer eteke efiesasete tedonerelistetet etn tateie (tat te pete ts 45, 82, 89
Gf INCI aAtiON Sais cere or tea RE Recon ereiotoncial terrence 41, 43, 83, 99, 100
}yo| 5:10 1s) ee GOE CoO DUM OOCGHOAGrN beso 5 cnope aoc oatotoancotocogedepcsnodoutoescd 61
WINES; TOO, ANEIE .2 5 Salers oa asete orahecels eter e eet SOS Cherie ore 83, 89, 91, 97, 98, 100, 101, 103
Area; relation: to weightand power. <2 as ssc joni cee erertatstoereteieistesieicrsiderieivel= 43, 44, 64, 90, 99, 101
supporting: \(seeiaiso Surface) ee ici iets orereneicicie ie heen eee teint eieseFotenstoseerietonet-ts 82, 87-89, 91, 93
ASHeESTOS; USE OLS oiace ccc scove re cieleschslexeteiers (eiche plots isolate ie joeePene ero re mae reloe Ea Veterofoneietarelele ier mete te terete 35, 63, 67
Associated Press, statement to................... ate Matas cha ier ond oars vetaie Srey sisyetagere al sual arctone eectnereerots 266, 280
Aviator equilibrium Of; ser cvercvetsis te oicvste erste ee aerePereTNe eeaieteiedoteteeroieioiokesoreielteieterctre tebe 161, 169, 253
WELSH 108 5 Schr. Rete west cleats ate vetey ote lak rete rove ole eestoners ers ate Peete teeter ciel eal nee tere ias 130, 210, 256
AWIATON’S: CAT ci 4:aie.ce Seevere s levareqars sjere Shershevolete afsterey = aieye role etseleictaveieTeeucicioce eee ieiereiriae 185-187, 214, 251, 252
JACK OU. oo. 5.5 crass apays, sr systerese ot elascesel aieder avons betetore lover clarshene reeves sVetetsvacetete stata (oehe Voters tata Eater sists ta bieteetete 273
Pic epoca cUpOno bh pone bab mooroacsodedope aus soa D0 Dp coo doc ONE Oho scgogsonehwassess 46 185
Us BAe oAnD spa ooRbonCnOEaore choc ouan sa boos soDdgoanOD serene 24d, 216, 265, 266, 272
B

Barcineg or pocketing of wings... 2.i.cc. nace tes cvetieatare easiest Sele cei etaerseete 84, 86, 100, 195, 203
Balance (see aiso: Cquilibritem)) lsc, eric teeters erties oaraie teenie ites crsrevensiae caekneterere etnies tetepetetetotate 82, 165
Balancing Of ACTOOTOnICY eto. < <5 parcels oie ee aoe eh eee eens 45-52, 81, 90, 109, 134, 211, 258
Git= br, Waa paa oO ooC OSD ODU UU OOUN COTO DOCA Do dogbauoUsSoccOdSenSaccas eee 246, 247
Nes Cn Go CE cheno merieoitcrdic conic dood doncadondosDaccGudtatoseno5000 . 211, 255
Ball-bearingsionsaunchine .cark. cer nc mice e nero enero eieicieteiotsereeicrs 160, 175, 177, 252, 253
BaMPOONLIPS LOL WANES eer rervetojelotealeetelete oeteke ral ste tte te eevee tere tetoleleveka levers ateloketakatel cel ste iste taietae= tease ie Teinte 200
Barometer; (amerold! essere wieie ate a rsroeue aie ora so wa oF orc rare eh eeatos ere orate lor eraye aeede eLS Renae ear meer eeeteteencieteleteye 186
Barus Drs Canlsboileriexperiments Dy: ciycryeceretectelerere eictereted ote stelels feustet-Fetoessboretavake acer 58, 70-75, 93-95
BathermeemenleCenic! <q. s,s 5)2cjeliewl- cas cise wse% 11, 24, 26, 27, 162, 212, 220-222, 237, 240, 241, 257, 262, 263
Bearings, ball, on aerodrome and launching car.............2.---2+2eeeceees 160, 175, 177, 252, 253
pronze on model acrodromes:2< </s, vetsiey-- ere cpeieey deter avelelcNciats) chet ake) slelcte Nie ieteene siete eeretapeteyslaheze 177
BO Ates Meier tircrere ase 55's coe oo 0.0 3.5, spe breve S cterarnieie nate levine satehole arsta loter ale jove iets ew ieietotetiretsirect 116, 168, 175, 273

“ Beehive” boilers (see boilers).
Bell; Alexander Graham 25.20% ccaya ssi cetevnceni lars seers ale bnienle ues ce atverepere cee nertahels 4, 96, 102-104, 106, 108
Bessemer steel guy: Wires. sec crocrosvere cg as eee Bae ere rede ee ate hate Ge relchateisiatonsccheredoie gestae Wetctatetals 172
13{c\¢:) (4-17) 4: re nS c singe scion tion odr er nOuDOMOMCIoCODStN cao pO AnAAOC oIS soo 174, 177, 241
Bird-winks; ‘CONStIUCtlON: “OL a5 ccsrecrsieee eles Kee tere ee eee eee ie nition een 7, 188, 200, 201
Birds; soarins,- Study: Ole «ccc cave ctec tetova ete vetelolarere ocho pe ere late erie er ei Antone rere rote 7, 9, 88, 287
Blazer,:S:M-,. engineer s-t< ac. icc cies cratete nei oe Gierere oreial oie oteielote lee creletsie level ol ale le stinleloqetotsteteretetatoted=| -tctereisTaleinta 126
“Bleeder,” feed! tube for Dune ec cite crore lciciescieicie ereueseveint tekovone erolebcloyelotelcteielotalcieialeletetetectet terete terete 67, 1138
Blériot:aeroplane'of Langley types so. ccrcre oc parictereie ie iotereineteieve storeistebaietoteletaieheteisersteceuicten pret perteks Bop ie
Blower‘ for ‘artificlal wind cicero cierto clove eioleteelei netaie telat ieee ieee ei oeieieieteie rite r reer care 61, 97, 225
Board of Ordnance and Fortification................- 124, 126, 132, 250, 255, 271, 276, 278, 279, 280
Boat; Nouse ss 3...2 5k chopsvisrecesa eis seen a ay ciate ele oa saan Peso ner er aremenerece 92, 93, 136, 148, 149, 156-163, 269
Body; construction of (see G10) WUT) crererocictorete oes cneteesloie Penederatetekeeteheltetetener cre state teteher esate teint fetes 32, 60
Boiler, “Beehive ”? type occ oe 6 gcc cscisvarsvora.cle ohaiwia arayud aim ol olaveletolsie oveletere tetei sieve leverstetsieverel evens a-ha eerste 34, 39
CON OF 6 F5.5 seys; 5 die peanizis oe ress reek SL ee arches Sictele ve fereiseereiet: ie ay Mee Teer 34-39, 70, 71, 113-116
development. Of e:.,cistisiis ani eliee eat ame eee ee eee ere 55-59, 65, 68, 70-75, 102, 114-116
DIESSULE © « ocieiece eee cial'erpnalevelel o.syererdel Masel ore a¥aieusta, a usteselersuereucis ane ane 58, 59, 63, 68, 69, 101, 102

report’ on, by Dri Baruss 2. eines seein Scloicrocorta olors dholeevaictose/oteVerstevcle Bonobanc (lari

no. 3 INDEX 311
Boiler—continued PAGE
SEDDOMGLELY DET i sicmrerehincivk Site cee Sea © eins oretecnts K DB sinis cemers ble rkieiasleletelviel ere w svaivnTe cle 56, 57
BULA YSU VIDE Becers eretaiatoloialelelanevois ever Cae aie tpl eps I RCI A oot EE eae 70
LOSES OLR ctaserete che cracencre vote ctsie cos oie oreo to teke SO ACT ne re CR Saeed, ae 70-75, 135
UD IESE OLA Sg: sre cacy eee a tas ses Nevoke fore oie ele TO SLSR ag 70-75, 114, 141
WATER UUDE MEM DOP Ole. sta eee nck Gk Sec ect ae eee oe ee es 34, 35, 70-75, 114
Bolometerhidevelopmentvoln cjg teehee ee ae ee eer a et Ea 123
STAKE eH OLSS-DOW ligne PRN a eins ene A oR 28, 37, 58, 61, 64-69, 117, 223, 224, 230, 233
EPL ORLY Dat atayatals ata aya acaraettcreste oie ee aerate ee 38, 61, 65, 66, 117, 179, 222, 228, 233, 249
Brass, USE NOL srefetspernstcrerereretsl ths oe aie it ora eres PN Peleg te lay ella 54, 63, 113, 180
LEW ANTES 3 Sicicienate ie pene ery eRe Mae Tye Ads eit Ae oth Va retail Seid DAE b 117, 173, 176, 235, 236
BEOUZC a LGU vars Meese emit ero steamer es eae 114, 116, 171, 173, 177, 234, 237-240
Burners, Bunsen type Pfopevs fer et es eum ete \anayone)lelesliane (0, sibievet aratviel at atsia'ialeTel eterete, otal am etriaiei tral atavarciete ave wen eR ean Dre eLilice
BasOhne. ae cke kiran sare Soho ae none ee 56, 60, 61, 62, 65, 67, 68, 70-75, 112-116, 149
STVCLOR LOM mAs, Coste stealer Se ate Gis ARO O RE A ACETATE Et ee ee 60, 67, 95, 115
RUS HIT SCS ULL ONE 1a yoy: fey ores oc eye oe iay Silanes aie ae en TOOT ST os ge 114-117, 121
BUZZan Oe Anon) Can An dens John Crowe StuidyaOLecere se eis areierncrater ei enereter eine erence nnn 285
Cc
Gamprasimtelephotaiper-viris sac eve rescore ots coef aiatatece oes gat ey siavee oR av otete ER ST ke 260, 261, 273
me CADMAS COVELCU “EDLODEIIONS ey eieye ace cies tecche trai oe civ al roeetate orarey arr STI TO A ee 84, 178
(CEI SEN AEN HONS TS os er eaaicesled trgegth Oe Fun eas ee me ta Renee Dae SONS ee yO ee leet lee 185-187, 214, 251, 252
launching (see launching apparatus).
Ganhbonenereyideveloped) byathe use vol... ocaicee dc ae cites soe mee aoe et eee eee 27
Carbonic-acidveascas, MotlverpOWeLe wast sce ae cn netics e slocicoe ie mcnice eine 11, 24, 26, 28, 29, 39, 53, 54
1OYC (Is Ae Serre IoC aoc ric ior Tao eee ATG Hoda ana Acoma cA mOaccentno cued mac 24, 28
PNEOZIN EVOL) creraysin shale w sfecaaie.shysia terion eee ener eee ee eae 28-29
Ratent) Neat OLE 3 sia dis misiatare ste erat ae eras OPO ohare Popes PA aan eae ee a ee 28
Carburetor, development of, suitable type of.............. 224, 225, 239, 240, 248, 249, 251, 253, 259
Carpenters nrankiG= switnesses: fiShtss< a sic sere wares neeenlone oon oa Oe oe ee eee 108
CASITOM MISE is CS CONQ1S Ob TON) are cyerciere cteteve ieee sci cunts salaries terete aan 114-117, 121, 234-236, 240
lS OL aie LD DAT AL US st ratati cn as ara roYateysi Sr cus\eresouthe e Siarats aslele\ Situs, bibbs ee Rare coatee eect ote ee eae eee eae oie 96, 110
Wentersoheonavitye gente carves niece cerns 10, 13-16, 45-52, 61, 64, 80, 91, 103, 148, 144, 150, 209, 210
inurelakongtO pLressuLredas sa. oaceeiscecmicce 10, 11, 15, 46, 48, 64, 98, 99, 101, 103
LCSSULE eye csc rce attue ons fe te eyons 7, 10, 11, 13, 15, 45-52, 78, 80, 84, 87, 88, 90, 91, 200, 209, 210
LOTTA Gs TO Toe siers ararn eye ciayeieucteteterese oe eucie Gy ehayeie!a Stan ae Para ee een RE Seroee 49, 87, 88, 90
NS AUEY Ac CHOLES TEN (ee OOS CROMER DAUD GOREUe cent hanc doc son DC aeb acme She Se odeospoeton 16
OPAL ODM a a: Nevapete si sicysie?=is(syh sceiatevstelstsc aieiatabclonste Ore ocean ie Sree toe etic arSteye Ricerca ieee nese 62
WINGERS 6.0 45 ee GD SDC AC ROCIO CL CORN aa SEE AD TS Conc o UH tet ObDG Ob onoeeser FOS 62
Gentrisn eal p wna rey eacie ev scr-toteleieray fo ates ane ls crave ne, Re pore ote eae are ete See eee 241, 248
Game Gallas mLuUelereravssctve ste 2, se eft aistais Suh cy sys; «evar as Sate eyes hm, ere Peltor Peta Pe A TENE eR eran Ree aa Tt ee 57
China silk (see silk).
Ghopawamsicnisland, ee otomacyEVierty..ccicieisvci: otelelorele bore eichel clelsla oicheletaieeneneatietee cee 93, 135, 153, 183, 256
Chronograph) attachments sevice s savers cishes oc icla 0) ave core ier Sow cyeteteraesPela eiaietetera nia sree eee iaeieineiaiee = 162, 163, 229
(CHU ANIERA GIT? e110) Chae Se Seer o Ec che Coie cach ey CRIES eGR MC CO ICO oerris GUS oma cenS ae 114, 244
CLAMPS pe wil Braye ever ccavo rake Secu a etkls acaiie alowed weirs eine alens tole Pabayera: cichavove a aye ayer are Donte One re ee 82, 89, 145, 183
CoastrandeGeod etics Sunviey actevelerscc cv usoj2\ sca cco cle/sve le disiara.cte ie Grolec elelore ere atetee clereterele crctetee eee 93, 145, 256
Goe#hetentis Ola Claseie tyr cesta cise a «ace Woterdy oravelele arelele Siotalera ecole cha -cfesete vara trek are Pai nian eralav ava ortaenerele ere mies 146
Coil, spark (see sparking devices).
(Glovers) sie U leery oe OP Gerace Bal ORC Ome OPE De OU Odo CERIO CUO OCCUCHUCL otic Ute ico 24, 25-26, 68, 112, 113
WoandenserN SUGa ris Feros sare taratiolley ray ct'dray te re voter alere ales eee eile, ot Sates herrotiote ietey aetcnet cs oper ayicl-cl aha yatta niet eater se ovate 65
@Gonstruction-and tests of large’ eneime’ 2%. cfalaecs. area: a can erst ars wareave.e eistale wieric ele: a¥a,acae ole! etppelelerers ele 234-250
Construction ‘of frame and “eneimes) sicccie cco aclevsistc otgsciar syove foie) blereve elas alts aya) a eis seile eter svene dle) elorehe ces 53-80
Of Jarre eyACKOGNOMTG thera,ccaickeve penta: aicbareiate cicrsteisia olehare slavereictale/eleicieetetelerercte 164-187
SUPDOFtINE SUPLACES: ..cas cine ts <tervoletorers sc sere susie cleyeisyayeraleratcle to /arciole niin uieleterereole © 188-206
Control wequilapriumns yan) Ser, neroricectatass stoetcrer-tecetas col at Neretoretcl iets torversteseateie eieserets. cle Ste iere 77, 78, 119, 207-217
VROSCODIC Bors ccs ota Yo a Ate ia crore sare atone heres vote decaretel sicher eiseseicinjclme cistersieiel o1m ceive shane, elelehalerele 78, 211
Cooling systems (see water and air cooling).
(QE ad rUElh OF Ont ecomcas Abopon Ob on dc obnoUaspodpeeAcdme cob enoonoRmoANans 27, 39, 63, 72, 112-115, 162
(Chayayaysye THEE oo ono cece Hite ccmmUo DOO CODON CCceeEn ADC HHUnodce 35, 56, 57, 59, 112, 115, 140, 141, 248
CYT eh S PAeG E AP OO rn eA iamiCn pe odo. Gace ene RDO RCC Cie nig OC Do AIGIO A cic 62, 120, 185, 243, 249
DTODCIVCTS terete ois pa oa evel oe ea prictcy staat Reta’ Mala sete eee ere tastes arctic thy alate hee heme ore t a pt ciate ate @ 178
Govenins elon wees te cre: aera apekey st cdstarel os chavshal <a) ovata (ei sraparol af ohare povaarstesa-ehasteyeter ohare: cr Neh ove cerca ane alerois eietevels ip 86, 103
VUES cos crarvclezatnis avarsiehs cease rspcteter scat yore apes 54, 63, 77, 81, 86, 88, 90, 148, 194, 195, 205
Gira nike pelle tery oe cpstete irc osteo vane foe toe ata fe et ct PM ered ota) sect evel MN ajiet bios ey pres anetotauey ata: het ehsvetels vei aries we! eete = 110

GIR NE eitig gyri GEICO CIC CO CECRIETIG UOC BIECCIDCOHODOLEE CO UCO RON UDOL DOO MOOU OOOO ICOnTAS: .. 244

312 INDEX vou. 27

PAGE
Crank-pin : <oso:-1o store wies olatareorats 5 ak ca a tara WI Te ote ai ecarared eeteastareraied etka aistalelal hate cietelaretastatets .ee- 237-239, 243-247
Crank-shatt: 202 v ves ae bets ee eles ene OO EEE aie een einen 237, 239, 244-246, 250
Cube; law of thew .ros.. 2 scree eticele mie ete alee atte ete re ie atest racist settee ete ae 129, 130, 222, 244, 249
Gurrie; Rolla. P;, ceport on American Buzzandeney-aeeterrietetaeidelieiierstep teeta recttatet=t Sat bien eee.
Gurved surfaces (see also wine (Curvature)! or cies cio cisieteieieletetolstesveleleleyscsetstatelaiseeneiote 18, 44, 46, 47, 99
Cylinders (see also engines, cylinders).
alumiinumlin) Construction OL= core <taiorsiehar elevotelaysieisielerele betel oteieieieteheierelcieaetoieelotetet terete tenants 114
brass*in iconstruction® Of% << cjieisc crore 21s lozayerecasde Shey ctatotel ste tavenel otal terotarah el tekalatl teeter steer telat ates
ICU) MAM BSA SHA Sem Samm DmaoUr A dso OvooUSddodMson OG 116, 121, 234, 235, 239, 240
construction! ‘Of. <.2.s.c. cere en ale ci eie al vrei 112, 114, 116, 121, 212, 213, 282, 235, 239, 240, 246
FEVE, EME INE: fates cc oo cis w ores welereyeravole axe) efateretoherey lice voter hetershexe tern shcterstohalaleietretayons 245, 246, 250, 255
HISH=PLESSUTe! Leys ieeis loves) aleleieve wey cte hela teletehal ale retey tev aneoroeee kel Medeteda tet atetafedeletatarefdeteretelekota feet kete totes 33
LOW=DLESSUTE! (2 aie wie wiciole va ele le ararerenorecerer oh notte reel neve ataenete tstavetocctiede texte ntotetete te etetersts tar steteta d= tetetetede 33
manltiple; engines. is. syscs elo sete ele otaketas cna persbecebol crehsdebste Reds rere terete yee te tote ee te ketene nee ete teee tee meeatatetiote 226
OsCillahing Fos ck exeisieca Sere oh okwre ore oreo St erste volaovets totale tetera tobepebtabet atest oielataiat certains 33, 38
tests. of (see also. engine: tests). ssnos c cleice a2 > crietos ein iohelasaietetarenshetate rata tetstiotel steaatete =p suarcte stata 55
WALLIS SOL: 252s so: 5yuie's- sie ais -alevaovaleraveneh tiaiovoreictek okays senlaveverstozele cata lctetelelsteieieinietotee recone hice ton iometens 239
(ct 4 1) Gene coco noone Don obo roboonodocopadeagdason nn aomaninanss 246, 247, 250
D

Daniell, on energy. in storage batteries er cierto el) eieeicis aie ete feletoredetetor siete sEoeboOCSOGOGHORS aieieieteten, eae!
Data SHEEtS soi). cis crore oe isle wis saave ave oretarcvenst oleiavateiolore inicvelel sie cieie okedeiaete ebay RoC tates ote inte teteio tei tet eteacnetea 297
Definitions: of terms.‘and: SYMDOIS* o..- sicjerese skepessvs role toke lala atelecea er ateratele ote arelot chee ete tele tov stetriets Tteteetare 14, 15
Deflection; absences0f* « << cop. custe sce eroleieye ators iessialevesepejatene inicio Tordelotoner-loreieiele eaeteiseieieea tae tcaeinie oieteieteteet 269
de Lucy; on sustaining Surfaces’ cjem.jereeter-io1eielevorolerolsnetetotstelstaseltolebetelatenststetstets [ovsteketeialststalat= teint natal tte 19
Diedral angle Of WINES earners, cctereroratoetey cl talevotsiererereseielederentieteletetstetstal tererereketete 45, 82, 88, 85, 89, 96, 146

Dimensions (see aerodrome descriptions and data sheets).
Distance mOL HiShts a. ctype ceretetsl-fortate terete eect aebetcioreer ti reeren keer tctery 108, 107-109, 135-155, 258
Distortion® Of “WAS. 3.55.5 syle. cyeg eterescuc sa cle laveolegersterevete voleyeir. eke olate svete foyelefnin rey aseretstal tals 82-84, 91, 98, 105
PTY. DATO LLCS i reic erste ccvalaraiare = c/a) =/sforer si oterol sla/ovelolelemerevetoeetotetstenetelobete keteleketslet ayer tel eels taliol helt Palate: fetetet se tetnttoet- toed 262
Duration: of Mights' (see: a1so) time) are, cicier ie leccteie sete elate miele vete lets! oneretayale 103, 107, 108, 137, 145, 148, 258
IDVarekMKN eV! ade nn ongagqdaD aon docoor od soscdonoUsDORONS AOR 222, 228, 229, 230, 242, 247, 249

E

Eagle quill and spruce rib, comparative strength of................. 0.00 c cece en ence ae aie Pa ceieteterm 2OUs
Harly steam Motors And OLOEIyMOGE] SS cere yer ale se = ted oder a lotreto = layer hs yatlats als alate ale ated ete fet oleh ah ols alot aetat at 30-40
HOMICLEN Cy: (OL GWAR Sire che ere tetctete lore rere erel oleh etotolelokote onnieinte eietatoierelenedeteoneietoreneestnote lteter 87, 89, 91, 144, 192, 193
Mishth'size mod Gls serecetecicicte cio cietoeretrersieretone Wa niclets (oie ieie area aveKote ie eerste Late iache ees oe eS 133, 134, 154
Blastie: limit. of Tiber area’ cysretete reac eo ete sete vacate ta ke tote re te tatea ce bats Pavement aie erate nate delatetayate realtone Shizgiens
lita lagen loo goapodoudasacc Du sonocaeD SoDao son coodcnandonodooDoscooUEanoeS 78, 90, 144, 152
Coefficient: OL i idicfa take sieteeiolaceiofe is so Shere tas fe seta epee tale ebatesstepebelovckeve rab iat vevatayeyaianat stations tate 51, 144, 146
Mlectric: batteries) snk Sco ace ete ecelavors oie taiaic elev ote > eee otoas toho rate a revoke tele Ie fore ictener ode raterete 24, 26, 27, 212, 262, 263
(bye tl: Ee ee Aa abe combo maGuD om ood ob 7GOs000 baa SG 70, 212, 220-223, 237, 241, 257
Hlectricity as Motive POWeMs aoc. 1ase1s.cvstavelal= iw loietass) ods clebeleetelole leone tet steyetelefenattelate fefereteteete nia t=tntrysioteteiot= 24, 26-28
Bnergy in foot Pounds; (SEE: ALSO MEL) aperers oysters Sete tele ete eee eke ee ena see a alee eed cael 23-27
Engine: (see.also motors)! 0.5 sc oe om «etnies ele sie ee 112-116, 179, 180, 222-225, 226-233, 234-250, 281
American. builders: < 22 adie sc coer rotors eee eee cee efededatede colesel>)chserseeietcteieeret= 131, 180, 219, 228
het) (0 Pin eAn An Oo OCUGOa UT oO On taSOO0d Loc o.6 EOOndoD SOs DS eon DAO SH OSU sao 226
MUtOMODHI le: of. co se wee avers corsa Sieve we eransinva) choise elaleetele otalopeketel el otciads felis laeteleffetete\atelstefePetaretetnyoperers = 219
balancing: 08 aac... so. ceteceee cone Cee Shae glectlevene Crane CATS RRO NIT ete 246, 247
ecarbonic-acid' gas. <.c7\siajcevatec cloeiecetaciol ocsiele niciayeleteletomlsletenetercle fee peteletetetetate [oteteveleteteteaetetatate 24, 26-29
compressed ‘ainsi. ccterrslevore csietestele wie oitolletel stele iota Oraetaieta cle tele otet aleveiarateteNaketer 11, 24-26, 68, 112
construction’ of, and frames) a. cere elec cere eee ieienieleleleiadetretehetersiers 53-79, 114, 116, 219, 223-233
Loto k: nS ee area AS OISMiCo AOA DODO oc ad ObEdoaonoUGoOO 234-250
(Oy sa Can () Jt ieee a See en Ame DA arid BOOS OSDSDOO SOD STOMCNO NS omoOOdCOO60 126
cylindersxof <i. cis esenies 33, 38, 54, 112, 114-116, 121, 212, 218, 232, 235-239, 246, 250, 255
description! of (one-Horse-pOW.er, sje: cree rele e telete dete ered aisle nerotels ohoyeic ete tokstal stelle tote feteie ret tet 37, 116
(111i 9 Sm AMC oMTOreMconoGronOnso notre oo DdaacotbopodvoDDOOdasTOGUTO BOC 000 24, 26-28
Nuropean Dulilderss <6, 2 crete ee rerieisletederale lee tete ete telee ele telyoheeeleee vale tetaetatedecete etree 131, 140, 219, 234
experimental sc Ai e/cleree ctovwte arcyese'e le to velsvwlete leveuenete evel siopensiohevetonef=tars(Relereletete! iatatatatets teks ieee tate 218-225
five-cylinder: © os.oics sine cist atcelerers inte cteis cee eeleeeiel et eiie cee ete eieeeiieters 224, 232, 234-250, 255
gas (see. diso gasoline’) Cy. aie ejsheveocotenehess leloetate eee lepetateionsteyet hereto ke ketal roles ete 26, 28, 131, 133
Gasoline i epeimeceneure seers eee 24, 37, 65, 125, 181, 179, 210, 218, 219, 224, 277

BUNDO WHER foie io oie jeictelciele vinieyolo rewstete etetelercietsictete eee felekaleraistoretotnets sieleloveloieisteretaistatate aiseente ee ewe SO eD.

Nae e

no. 3 INDEX 313
Engine—continued ron
horse-power (see also brake, horse-power) ...........secccccercceccccccece 37, 58, 116 233
AGUA RCTS iodo SED OEROC GOOSEN PIS IPE son pay a a ee wee Py Lees 24, 25, 68
large, construction BNCELCRESY OL. arararetaeyaiate co yoeietaiste ee Ma IASI Ione tread 133, 234-250, 281, 282
WLP H GRO liprsin Muvercte ties, cpevse Ale erore ie aie Scar Sete Eee Ee eee ee 247, 250, 256
WIDINNT* 6 SoC 0 EROS LOC ROTO OLE ae GAR ad AOI tie On OOO a Maas eet eo Gane 219-225
PUMDLGH GMC UMN CL Re ternad tr evscacs ic is ai. cus hsbay ev asoraleistote ane stoner ecoTs, prota @ er rtaere REE serene ino cea aie 226
COTE Lt tA A eer ey Aoto GIO OMIA Tanne ACCT Ath a RA eR eR aS At tren ni 33, 38
TRIGA OS “ea Oa Og COC GCOC SE CE OR not RE CoM can eee mCi EST coma a owimdc ‘952
EGR, Cyn cad arco OO LOO DICOe HEE OC AGH On ARBOR cmPoic scat are 24, 30-40, 64, 69, 116, 120
AIMTENSLONS OLE e ays porsche: sek oho: oiceades ake bay ele cehetoye o” overctura Ore teiae oltarhe Mi oid arate Sa eters ly aicg eee 116
Stringfellow 30, 31
USE oc 5 Ont uc BA IOCROG COCR IRE RISE Ice 37, 55, 61, 69, 102, 133, 148, 234-250, 281, 282
Maree Het COlO OU abareneetnete ort eleinayerasic Ste .c lakve is elite wtundie eitete eieiahe es ieee 220, 235, 236, 241, 247, 248, 252
WiGIEL (Gin oo op aod GSU OIG OC Orch Cee Onn mc Reo anc ar micrc 116, 126, 130, 209, 247, 250
ENC UMETD ULI AIL ALTA OT AT CO} Ole tsccleie ay siczerele ls ie) vie ie iele nvare'e o's fey eieie ellcheselescisielerere etela\e 6, 31, 45, 51, 144, 213-216
WRT UMA ALO Le Fetsye thaletere ea Vove a cree arson, are sho ni’el beni Gabe Koma mee oie the! o etallatermeisderele 161, 169, 213, 253
AN ee COMET OMe rossyey ch avey acts. oc! onl ceeus rot ov orettus joi alopateer sncravay aye }ayaseestei.s avasiesate: salsl pve 77, 78, 119, 207-217
lateral wandeloneitudinalestabllityicnvercve crete acres icie.cle/s-c oielclerein) cve)sieiclcla)stetelatalordiaterets 31, 45-52
MCA NOLAuLOM aT UCROLM PAB OIL Oar ys vert si scteycie aicers svercaclocleta « piereuers irae hoicyauciay sia heyanlatotane setae icone ratetete 65, 66
TOKIO KOS ES - Goce coe G4 a8 arc CODIRO CG GUO OUD OUDDU Gop moO GCDUD COOOL OGUDGROULCC act 37, 65, 67, 114, 148
F
SnD CLG La ORS ALO Uyaee Hebert rarer cic ee cyan tevenc ciesevsesicvai'e ince efeiaees sal svavetel Siet eusievaiieic alelote o otese, cteterarstela etateteretate 111, 186
GRU GES MEDELITE Van Lame myterara tic cis or ceicrei orate, ois coke oeswicioceru iaielistoye syajalofaiwine ofale ssi aver astavetovaueteyaleretatemiats 188, 200
LOvepLOpelilersDlades made sOl ae ete las <tercbat= =\eu-/ol ele (ole) lol» atnlore eel \eleleelb/ulel see lola |s/='slslmfelalsvelpiavale 8
GCC ORET AVAIL VaRee tet ter tete rcfetepetereteiciasciel oie cae cic tici sl cheraueievas rs siete stelaje ct slcvertl sla'a) ofetalelale o(elatelolelelalvieiete aJensleentals 239
IMTS. TO ETAO) S oc co OO AEOIO OnE SO ae os See Ga Rone I GnoeDO dio cortue pe tocrmortio SUcaccd.aceot 241, 257
Field trials, eighth-size 33, 134, 154
large and quarto size models................-..---- 126, 158, 170, 181, 226-234, 255-282
TAO OI SHIN OS MO tal mie wie evaiereataterer ouch choses ela si e(alete: si nyelelate slalialai+icleleuetsloieret= olnseieln/aletelaiel o!si= 29, 53
INGE GY Wao. doads4 0G Cobb obp os SUM ope PUpoD FoGOBUDOCUaOGO cemooncoaus 63, 92-106
Wash lip. cgrcou obs de ap OCHD Ose sOROAOADOOO Comc.octro 2, 61, 79, 135-155, 231, 257
Hme-prootin Sj prepar acl OW ce vcrsleieieys ec= oes l-veve = ols wlelellelese in « mn) olnicreie\s bajeis's «a s)ole/mieile civlels)nic eimisi= ial 7 148
First flight of heavier than air machine.......... 6... eee ee eee eee ee eee eee eet eee eee 107, 108
First trial of a flying-machine in free air........- 2 eect eee eee ee eter teeter eee eee eees 97
Diereeas Che TN Goo cacdace dues ued Doe bcne aconon BUC uSOCONno ToC DUCGo CO OOOODOOCORGTOK 82-84, 91, 98, 105
Flight (see aerodrome and aerodrome mode! flights).
PINGS EUG. OM vere ore eetleiere cletelcte.sisi< @!=/~ieo\el Sl =) nu-\oleleie © ele:oieln/s/ein\s1 0/012) =1816) se tcee cesses eet esees
Gt TEVANS: TMGVE Ney So 5 beuolerooo om codon e Does pon odecObDODons t000 SOO DUSrEDInOd 126 55-
Wik? (hy IIR aoog cob eueoudoBRoOnbE abodU Us CaGDDEUUCCR OO ODcUs OConORmon iOmrcn. Peay
models INoS4) 5, Bow. occ cc dere wc cee cece see cenesscencsinn sae 2, 63, 79, 92-109,
Gt GAS mi Pebsseosnease appeODs eS CeuED bo +o od DOU cou Obnd doa CUODOODOUCuomonr
TUPDETLa Liv-CUMOUG!S sete s cleicie cre © clelaicrefole © ele -reielel=\01 »in}seis1=|-l-lelal=)e>irisini= (i=) nr cete :
quarter-size models .........-+-.+--seetee reece 158, 170, 226-233, 243, 2
LOa tad Sant Meum OC CIS Miirere cy ster lane sis uel cle ere © aleistciels!={eleie et> clnle|elaiai=isiaje) ele arminiele\ 64, 68, 69, 99,
Eulivswitce [Su Omen ime weet reir gehurctetel foie acre lols wialsioie nfsl sivaele.-lol=\nlnlei~yuleleiaislem\elini*/sin) siaiciciccols 242,
WMlyiney aerodrome -MOGel asia Kite fare) ~~ -tnselmn cle wie sel im imeialnin sna 2 wo ris hisieleisjeicie Sone sins
Flying-weight of aerodromes (see also data sheets ) ib, 62: 63) 76), 77, 81, O92) 91, 148; 6
Dlpigaowials, GIN GE goconceodsgebadbaa ouoomo cose C ODD Osu CUO UDer SIG OOS GIO OIU OLB CEO] 2 15
energy in (see also horse-POWEL) ....--- +--+ +e eee este etter eet t tsetse Pie 62
TROOEOELI). ou Gu gob GoHAe ope DON oeeeSNEOdd OR 02 Gnd 960 OdDUPnD a TON OC COO RODOI ODS OCR G OL CAS 57
Formule:
PEG ta ae ncn PERO D Or DRE ODE RODD OR AS Sit GEICid SDT fae BC OOD OO IOLA ICAO TCO T Othe 19
(SO Chk TECK HOD ORO COCO CDOT Ono hd De OOO DD OURO DCO ODO UOLL 49, 87, 88, 90, 101
Gi. Ge ceaks cae Use co ODODE UbOO OC UO CTORUC One eDOr ane Dn OOS DEO ReaD COO UIE DEE 41, 43
ATIBIANE Ba pSabdaadacan sa cad esateton apes e Ch Se nEaOe Goa ER ce AGH OSC OS Of ORG 47
EIA ARIES cos shee ooo ete oddone oD Oh ouidicvc ans CAME MDC Uo mtu Uke GOO IS2e 19
TROBE Giet Abesea moa os pou c Manon go cba MOUdEn ORD Cae SOOO OOCR MSE ISO orn GTI 15, 62
it Gio WERE Ske cles ode do so Boca oOo POU bias SOMO DD EDU OO SOTO CORD COTE REIS U 41, 43, 62
Manly’s, for changing center of pressure......--+-+-+++sereertrs tert r sete t eset ese s es 51
IMARCITES eLOLENOLSE TO WELe ies srsyiarsiotatelnsters al -Vnicloiere vinlajerncn elelaimiwiciet sie imho) oieicm -icimclcishs Aisi 15
RETNA "HSs acs sae code cov 6 Or DU Dame S OE DOU GOO cri 0 Oo ir Raa Ie Sar Fa
REAMINE NSO. Casuint ogres Cae con O0b aeRO Deon an Urey OM Sita DOGG Ta rs iii Sa =
PANTO TITTIES Si apctelerciein ooo eerwle avel oe! ojafele © syeisisi= ele 18, 23, 97, 62

WOLK (SEE GISO NOTSP-POWEF))... 6-2 ec e eat eee aceiacerseccnctetesrrctmoecs

314 INDEX vou. 27
PAGE
Frame, construction: Of) model's eter ei lecete =r ftedeis ae ots eae sind eileen alent 89, 53-80, 90, 112, 119, 129
Tare ACTOCTOME. ce cease cucy ato) arsiete ein hele Lebar recon stata ere aie en eet tines 164-187, 253
rit hh) i ee arin MeSGm AO Gad vcd canbadcnoduonohaoKoot a eons 165-168, 170
TESistanece OL coc ce sk wie Sie nsw eaten 0.6 ele ei, Oe elo ait era Sabah eae Tale Sten eCANeEa Te ever piste ci ere tite ren et oiere 165-167
testing «Of occa ete ces ere se a retehe ere ee el Se aaa eel ota ah alin ea aes eatin eee er ae ROR SERS 79
ETANSVETSE: < 5.2 5b ccs ona Sere ove oe SE eee eT Och one een ees creo eee 77, 165, 174-178
4 (0) ero ran tia riccitouidcttoncocndcobc ocodduconstquacascuDagoubonoteoeopedaodas 118
HNrench Academy, communication! tos c.<ic.< cise so zisi-iareieis isle roebeverepere eierauny eva elders tavern cit eee ae eae 3
Ruel -alecoholand hydrocarbon: se.:oe science eC eer ieeneie DY PA Boa Dilly W104 45 183
CANDO ace 505 505,55 a eis eshte b5s5y 5 Saye ayaarey s aleve ovale el yates otede tabovehets aueta rete letetehs fevebeyeno bee rei te t= feeeeete aaa 27
carbonic’ acid'2asiccx circ csi crsiate Sons spareiers is en rain ea haieiers SANE 11, 24, 26, 28, 29, 39, 53, 54
CHATCOAD 555i 5 Sissciels wie Sie saie os a tesaieve,a) aye 3 ren sgereieh ay ardpeta repel evepete enero rate araeokae era ae As etree cians eerie 57
Cee ee mransricrerrict Tor Gnciccdomn otic onoododbbaLCS GUSbdeloodduc< 26, 28, 37
@asoline iy... Nate s sac e cigs cee wae elem eae 24, 25, 36, 37, 65-68, 112, 125, 224. 248, 259
OCR SUh Zit) Sener ie Seen eneian csticn scorn ohuttict oben cud ¢osdod ssc bate ddecodgecen sts 68
Wuel stank 2h c.. sayaystea ie a,c Jolstec eae ols se eke he pape eee AS TOE aie Ciencia 36, 65, 67, 68, 112, 113
Munds for experiment sisisic'sic/e erosteve ero ciekere)sketetotereteheersuses tailor eetcneneroeieas 124-126, 132, 257, 278, 279, 281
G
Gaertner Mrs instrument maker: acres coveter acest ele reieleielelenenetsaere cloieletel oteladsiatere iene yeneterets Cc aetetterste 93) 95
Gas; Carbonic-acids «00222 -cccre vie stovttnle ejeketase i cletetetetetevate ay-teuelefetalael tel areketatal i= teieyaiotetis 24, 26, 28, 36, 68, 113
MAS-PULNETS Sopa peeve erates ecaraievors oatoyetenedetstel oho oraterer stars eleet niet taut ane tates enetebosetele 35, 55, 6U, 65, 70-75, 112, 113
Gas-engine (‘see also) engines, gas! and! Zasolime) eres seve leet < ee wictelelois cielo rete ieinle lotelotetssiate 26, 28, 37
iy higcmag bbl gear odcouondonondedocdoUedodchocndagogUOnOucdnOE DS cODDe 224, 234-250, 255
[Che AG Orne GOO OnOn aor On Oo aaoD od 60 DUddO domo goo DOO DODTaeGaeoI5 234-250, 277
bK)}'() GEER EHS SOOT sao Gora on rotoeotic ordabcd COnOSaauOaSeE 26-28, 65, 131, 183, 232-234
Gasoline-burnersy aero release estinto a cise ees OO aes 56, 60, 62, 65, 67, 68, 70-75, 112-116, 149
Gasoline-engines®. 5-2 acre en - ce nde eee 24, 37, 65, 125, 1381, 179, 210, 218-225, 232-234, 248, 259, 277
Gasoline-evaporator \..25:5, och pei eievooinra sister ETS) ST ao UE SOTO UeS TORO OS LTTE RT Se 37, 65, 148
Garis. tvercvcteye sitiorereeks eo CR eee Tale aly ales ley ale WES alba Pei Buhl
ribson,,Captain:,, record ems .:accea.c ose siotese dave Sissel dosfotelo eee ee Om. Sa CLO alo seraterav ohana act eT e eae ST Te Rona a 250
Goldbeater’s: ‘skin, ‘for’ “wins ieee <.c Ooe ae sate Hehe la sists CS ee LE eee Cee eee 77
Goode; ! GF BLOWN srs coos yes = ce Peewee eer es eS ea geo ne Se SI ese raas Yee aeons 97
Government allotment (see also Board of Ordnance and Fortification)............. 124-126, 132, 279
Gravityzicentertofl co c\acsntceie 10, 18-16, 45-52, 61, 64, 80, $1, 98, 101, 103, 148, 144, 150, 209, 210
Gravity-feed: 2).5 (cis siasievels ai treme ele oe oe mee ety Mee eisai 6 IU Saree ee nei 23
juiding (see equilibrium and control; sustaining surfaces; and rudder).
Gumemetal. sioic i. soe aver cjevals orators ia teraie eieie: staves Gate ae ere are eee ee RCI nT One Cae aoe 174
TUNDPOW GEN. «. dase see ee hele ere Soave Sidha Sha rerate gS aieyelcnel oeoea BU SION ore, Coke Se eee Hare eee 24, 25
Guysposts io stiote ayo et eee etamere oneal cos ictet SoC ae nee 184, 189, 199, 266, 267, 268, 270, 274, 275
Guying; early wsystems ofr: cc laie oocis bers cites asta eee eee ea ere eee eee 81, 84-91
DUC EE MRE RD an ton © NODS OAnCT OD oO 81, 84-90, 99, 164-178, 189, 191, 196, 199, 264, 266
Gyroscopic: control! sh. -<saictare vies atue atte. eis ole rerore lols ror thale ekoie tote ole aes eater eee 78, 211
H
Harting’s: formula; f smiesics< sissies oo ccc notes COC eee eee On EEE CEE eC Eee Eee 19
Head “resistance: ).[3:s0<,.ciscahe = cscveve, cintatatersle era iotevors lovee tas ection a ee eee nes 142, 165-167
Heating apparatus (see burners).
Herring, A.-M, ‘assistant > 5; 52.245 .ccrata slece coos erste soe Sree aaa ye AIS ere 104
Hewitt,.Mr.):at rescue of NirsManly s.ccsfacca ie ee eine eek eee ne ee eee 273
Hodgkin's fund; ‘aid from’. 2c... ise oo ari ee ae ee ee ee 257
Flolmes, Wits sc Scinta cis miaeesion Weenie Ge an Ee Ona Ee CER On Seon: See ee eee 286, 289
Horizontal! fight, velocity, required! tosustainacon ene een eee 1, 116-19, 43) 91
Gs) Sane SoCo O Ae net on: On onoomnoiin Gos not cianbondoudabauocmcdcon 8
Horse-power, (exerted bycrubbersccse aece en eee eee 9, 22
Maxim's: formulas 5: ¥.wjoc acces Sate oN eA Oe eae 15
required. 'to sustain filght.23\.ccqoces 2 Soe ee Oe ee eee tl
developed® si. sc2242 eae ace eee 28, 37, 55, 58, 64-69, 117, 179, 223, 233, 249
Hot-water emeine’ co... 6) cdinscvascaitios ate lore ceive tol eee oe ee ee 24, 25
House-boat and launching apparatus........................ 92-109, 110-122, 148, 149, 156, 163, 269
Huffaker, BiG co aa etcieyscte ete no ee ee ee ee ene 44, 46
Hull construction ofa eee eee o ES ony ete 30) 32) S65 1bS) CONGO ibe diliarsladioatioan
forms a inne COe eC Prn DHT GGH One ae bor ae cobroUcee bance sco sabe 30, 31, 32, 38, 60, 69
TESIStANCE oye)e:sceisreaie srdhajeiard ae Sane sera eee LT oe oe eee ee ee 49, 69

x ado psinelbos He EOE He es ech eRee ane nn na ieee 39, 69, 75, 112, 118, 120

no. 3 INDEX 315
ate ; : I PAGE
gnition (see electric batteries and circuits).
Indiaimubher for power) (see also) rubber), ..\-...<+.0 02s cance alsieicciesisieretiee + 21, 40
[incited SRC Ra Utena eC enue im Le an 6, 42
Inclination, angie nC GRE eee ee Pm Ts Meee Bie eR errs eter ah
iigrs7il GIT ac ce OI a a MR TREE Tc Pecan nd Le CAE PUA NS 4. 144, 241, 257
0.0) 6 v,0-W eu b0/0 p 0's 9.0 elute ties «o'er 6 emo. 6.0%: eFllelu a piece 44, 241, 40
IRD, DE) Wr oh oooscanbecnochoUSUooODOU doodbNchoos wrbodooouegennc dap 63, 64, 114-117, 234, 236, 240
J
alae otinm GOL AVA ALOLISU cree oyare! ce tre cleracatevere S crate oleieieienictaletsVassisyavelsts afevavotasleratetelate mieleteyeyeratshetate 273
e LCL ie aie acacia care ais odeiat ove <idierei wi Sr anede ekofereimienehel suelepetan spt alel oils) hele fnivetia/y 220, 234, 236, 241. 247, 252
TOMMEOLOW 4 (DITG) OL J AINAICA) y SUUGY) OL se sieves epeicte ern cicl ein e'c eidisie Wis sieelaie «’ieiv\nis sn elalbin plea’ & ele\aiaia & 285
K
ARMIN OCC lel OMEGA sels cioielsiaiatelcicis ele-> islet eke/=[sie/alaletelslelefel wlelstelejs’ o/s) ei= ies sistajere: v/a! efa\s.s) olnse)sieinisizte 133, 154, 155
L

Langley, S. P....3, 4, 9, 18, 76-79, 93, 95, 102-108, 112, 123-126, 128, 131, 183, 1 53, 156, 161, 179,
183, 184, 188, 211, 212, 219, 223, 280, 281, 257, 266-268, 270, 271, 278, 280, 281.
RUALCIN OTD Of eerste to cisions cra caste ieiais nacuc ie atsisyoyelolete, siete colerelehefa. Vn olny fe lsseheys tcYelehalierstofote gieuner 124, 280

letter of instructions from (see appendix).

study of “ John Crow” bird (see appendix).

aerodrome, War Department report ON...........2 +e eee eee e eee eee tenes 277, 278, 279

“Langley type” of aerodrome ..........:.--+22--esseeeeeee ees 77, 164, 208, 244, 266, 276, 278-281

MUGS! Gramcsemeonnent/6b0n5 sn 00ROS0s quar acoenenoanotUeEcat 2oan9G0G00 77, 86

iL DUNN 5 on oo soobeodeeesene ce soDp Connor oc docospcnn -UpseCOdo Docs son 65 Go 0bMic 45-52, 97

Tiaunching, difficulties Of 2.2.5.6 eee ee ecg eee renee erence site eens 10; “il, 12; 925 94, 96, 99

TIAGO SHO Lane ere reais acco coe ace cielo lose) avatars ie loycfolers7e) felt Fusteps loleravohiile Lutete}~/ oleae eet ekaterete 13, 94-97, 110

of large machine ...........0.-esec cece seen sneer tess tees 265-267, 271-272, 276, 282

Launching-apparatus ..... 92-122, 134, 149, 156-163, 183, 185, 281, 257, 261, 265-267, 270, 272, 276, 282

OVeEHCAd fee eee 5, 92-122, 133-135, 139, 142, 143, 145, 151, 152, 154, 156-163

quae IN GAoeotesdoonss9esac9 134, 135, 145-147, 151, 152, 154, 156-163, 183

G(sny Gale ciel: IB Seam Hoe o be Dmmnn Coc oDDIO da TMot ron SOD OO RR OC O.ONCTS 265, 276, 282

Meant citi Caterer terretrel teistosey= stele sieieiaier ie 158. 159, 183, 184, 255, 258, 262, 266-268, 271, 272, 274, 277

Launching-speed (sce also velocity) ...---+---+++essrrr serene satelolclane lereielesewter= whevohayvers 135, 161, 162

TL GRy GRC HIG’ Clo scion woos des enep ean ovncouges padnoodoa sous cdoUmoDVon DRO DOCONCMORI ACD 129, 130

DEaie, Carman IDNao8 oauouanesd see epauddouanaa ode de upod Cesc pab oben osH Snooping aye t se 250

Lift of propellers (see also pendulum tests) ....61, 62, 66, 69, 77, 94, 99, 102, 105, 107, 151, 189, 192

Tilienthal. (Otto, on efficiency Of CUTVES..... 12 one ve eee we erect tee aciia rinse acl sias soa or 44

iUiGel MEIEOLA? cave boowsebae cobuse cues onbOObOsUonCHS COC DRG DrGLe GHopo Car ESS OLET 1, 43, 110, 166

Li lscrn eh boue Aw oule Sereic eae Nn Noein ag Rain or eeern eae aah pS na G CPs G2 SOUS Ge a apr 154

[eq ial myaile ET abt Manel do DCO Ceo eed ae UoMERnGe pao D oO CU IDC nace Cs 45-52

TDI T noo ge Go cpoau Coes bOuboer ocac uopadood (ib aphpoGasgo op pe VCOOGDp Soci 118, 177, 234, 2389, 240
M

ARO AIG clihe, abesenpoe Rondon oe poneaEeE OU UOREAt So OCCHOROOCORCDOOS OCIS COS e VRIES 266, 271, 272

INtoiinlevambres dent a wallllnetnste fete let=yeteleretelegersi sei - acini ek ciel Gale eas aes 123, 124

MEY, Neapel> Nie Wises) oan () Pogo oooeEAadsonodg dnc BOO ORDCCR COCR eGo 20000 298056 799K 53) 7: 276-278

IED VENT epM A CDINISt sie) sale\ose eee cre aiec lel ert iors os aoa Sioa ces sc earl 93-95, 102, 106

Man-carrying machine .....--++++++-+serrestts 123, 125, 129, 130, Loi, 153, 156-187, 234-250, 255-282

Manly, C. M., assistant in charge of experiments.....--. 123, 129, 218-224, 265, 266, 268, 272, 276, 278

Gitta Saeceeeeaotop eopererton as oonabocoac htc doe C Urn alon Gh ZU use RISC aT 219-225

Fey WL eo DEMO dob aos SOUDE Dane 6 CBA CRD BODOG SEAN OAC BHO upURE BORGO! 8 SAS 51

TGhemMe description of Ment. Wiper «ano sneha er meee ms ene 260-261

Aeaalanraiiorm ula tor HOTSe POWER ss <a =o sme ariore oman moose eee ye 15

MST onInA phick a Mee Lee nse tet dae omens yohewoniurre enn nae a 2-4

FAN Tretia alge pe ial atiiens BOee pene CEL OUR Pan MOG mr AD eUE RACE EGO. 9 e122 ie 1

IBYST Ie SUM sie, gh aennatn cogbU ant he GsUecRo gps GfaC OCR Osage CDEC AUS sc 5G 4

POI DENI EX: Giana sou cmaqnooriaon dot bbe Conor covoaur daar maa ChG Co anes 3-4

RARER CROT een res aoe estos yas bea eee Soho ee 63, 72, 115, 257

Models (see also aerodrome model description and trials). $

FL FSTOLTNSTN Eye tll BOC CDC Oa a CUO ace hana ian gene ia 1, 133-155

6-14, 17, 19

flight of (see trials).

316 INDEX vou. 27
Models—continued PAGE
launching of (see also launching apparatus) .................s--ceveceeeece . 92-122, 183, 134
rubber-driven <0. cae sc elsvie ctetecle o/ete ee nett aketevn ais erates AIS erietiags Stein) LD eS-2AT LEG
steam driven ((iseeaiso NOS 4, (5510) ererote ebasalcieteretedetedersteictetelteteteterehetetetetatatocatateratay= mloxereveretote 134, 135
steam, MOLOr,, ANG OUWER® <i <feiete cloister leletereielo) oho etate re atele ol tats toieteiet ttle teeta leita td siecle ees O0-40
Motive-power (see also engines, electricity, and fuel) ....................02---seees 8, 11, 21-29, 118
GiscussiOn Of veces caine coe boas ce oe conte Sitter cee eee iclace erro isiekers Siernieteelaroretonn | eee
Motors; available (see"a@lS07 CNS iNES) |< ore oe clateie area tel teln miedo tata avadelist stot ot etistinte otal at isis ete ets 11, 21-29, 278
Carbonic-acid Bas) <ichrec cee ee clone olen eee eel eede denen nee beicleroter a asia 11, 24, 26, 28, 29, 39, 53, 54
((ovehoyescUl Chbe Sanam san GooceUgdoonntoaenouidcanuqcudodgsodeson 11, 24, 25, 26, 68, 112; 113
construction of early types! OLS <5. cio sieve ce aie ole oe wlolle erelerelelataeloielatei tats (s1 «l= hui tet ela/elolnnlsiejatel-talar 30-40
Olectrical 25 Ce cic ete alae sic Renee eicier terete coveusherene stat ieverteten Reiter eienener 24, 26, 27, 212, 262, 263
BAS. iw octets era etter ave ensPeerete Gee apoio overs Clete eetetetoleketetoheteiRerstekeretel teystatatatet tees 26, 28, 37, 131, 137
FABOLING v arete oie atsicle eesre ene tiie tre eer 24, 37, 65, 125, 131, 179, 210, 218, 219, 224, 277
SUT POW CET: “aa le-cvecers ose ierele = /ete overstate levee etetetelelepesetevetedeketer eel =fatiats nce Rey stevota eal henate Caleta nioferheeiseeseaD
TROCAWAUOT score ors ele ore cig tele etuae eteretecene te ale aetaVete rel MekeVad ciel teierorofatetetcheiere ts retaker ten -feretaiefolecetetata 24, 25, 68
TUDDELR oo ciccce ers eects clear eeteras « a serenlol ata aioe l ste ietoteteseie det eletet keto tatalotaletetateiatate hiatal avevoretee ciate 5, 8-24, 76
SECA wr cte pole ie dos ordncne (Sono Pele Where os wie Fel epaterahans tenakelevevehevenelenolevetobeeretekete tere teketete tata neteteietet ella t- Fete 24-25, 30-40
weight of (see also weight of engines)................----+-+--- 116, 126, 130, 209, 247, 250
Mount whitney, observations ON. ..........ec cee rece e ener e eter reteset eecerssterercs cacao RB)
N
Nashe (Drs BS iliadiass. cts cvcieisieiere olcioyere steve eleioters er) clel ake kere tett Ne leeetelckonepe ten siohetelocaistetateatel ietele iter tetanat later 276
National Museum, models: imae -cvrecie oie siete ise ois eel woh Nieto ote Favelehe (al ala tokelied lint nketat ste tol hol rela teroteiatete teh eetetee 282
INeedle=val ve — oc.ouie eiiwreccrceiw ever cre clave! scl eve alnsale ois o/ehe feraleloieielisboretetctete tates <a etetstatntn lan Uai alana inet 56, 57, 113
Nitric: acid: USE ‘Of s<c.i--:asi< 6 wieisy suaetoveveielaletets toletere lelevapeuctcnrenstate1 ovenolelelefe Nel Ne ioetekei=lanehat a ienchele aieeTobo tale netonn 71
Nomenclature of parts Of 2eCrOdroOMe....... 1... eee cee cere eee eee teeter eect eter recs eccee 14, 15
oO
Oiling. Systemisip ho cie cts cake wtelsele cholo retrain cloree bode tere oe tonal reba oko = ous laanteolevelotalote tere 113, 177, 234, 239, 240
Open wind, experiments in. .........--. eee e eee ee ee ee eee etter neces 42, 99, 257, 271, 272
Ordnance and Fortification (see Board of).
Oxygen, mecessity Of ..... cece cece eee reer e tree cern este tere tase teeta eenecece rst eneesereeecese 72
ie
Paper covering for Trudder............-.2 cere eee e reece tenet ent e cece cen eserseeeserercs 86, 108
Pénaud, Alphonse, toy aeroplane designed Dy........-.+. ++ se se cece cece eee eee 7-9, 21, 22, 40
tail or rudder....8, 12, 13, 50, 51, 79, 82, 107, 122, 139-147, 151, 152, 158, 209, 211, 213, 214,
r 216, 253, 264, 270-272
“Pendulum, testetOlmilet eteieyslersherclafereiakelatelaleteteioler apatite rele 60, 61, 66, 94, 131, 135, 211, 212, 214, 232
Percaline for Wing COVETING...... 0... cee cee cece cece eee teen tte t eter e esses e se eeeesases 194, 195
Pinion (see gears). .
Piston (see engines and cylinders).
Pitch “of propellers’ cetera leew tole ie clelele) ole elsieleteletetaielobalo}ola\el hetalolelelotetahereheelefelsistsircraiciel 63, 69, 76, 94, 181
Plane (see also wings and surfaces).
GTOPPCT 25 ce wcere oie orev e/etere eiele,oeieleierelelnigcly lela ele lola sloieletepatataderuinte a ole [aiainvon= CY Toteieln Sloe 150
surface, angle of inclination of...............-.-eeee eee e ee eees 6, 8, 41-45, G1, 83, 97, 99, 100
velocity required to sustain.........-.--- 20 eee eee ee eee eee eee ee ees 1, 43, 110, 166
Pocketing: Of Wings. <<<. - oie olatela)e/aieleheloleleleloinie) sais Novo) ele(aatnta)=inlnjoleni=ieksi=siealersistansi= 84, 86, 100, 195, 203
Potomac River, location of testS ON.......-.-- eee e eee e erect teen ete re eee e tees cess saenene 93
Power (see also steam, fuel, and electricity).
evelopment Of se vec oe on cisielc ioe cioelerate wale <caiet slots! o\o otelolsioloNelwleislete = shel = hata mtess ier Soi ieee 8, 39
FOrMUIAa: LOT” oo re oicicccacrcce Hever coe 6 a a is Gies B)a1S ie © whe mtetntel wheteirele coral ateleletnne e-em hele teas eles ey lear meNal ate 62
generating apparatus ...........-... eccicls oie lesctatalele slo) #1a\e\ahn}ole/ofauarsuatetsisteyaneit ef Peio oko 112, 125
relation to area and weight... . 0... ce.cce0- nrc ween cece ee «mem mimici= enim tines ale)s)eie mele) aus/ oles 43
Power-gauge (see dynamometer).
Powell, Maior Gi Ei; TeCOTGEN ce er wick oie «cle efotetnte ote ole tesinte Colne tosolm ol Tale ait elaine 250, 267, 276
Press, attitude Of ce cc cece oc oto cries eile stele ezeint= sie imietnintalnfelagole oie nie lel sie seiko cia 127, 268
report to, Mr: Langley’s) <0. )c serie om -lolerere a tepels 9 feral ibet ie iets a a each lea cca aca 280
Mr: Manily’s: o..cccciecce einen sesle oie le sieves tole tenn ieteN lime esciciete) aston iee 266-267
Pressure, center of .......2.02.--- 7, 10, 11, 13, 15, 45-52, 64, 78, 80, 84, 87, 88. 90, 91, 200, 209, 210
rules. for locating. «0.0% ocn% ecm « mmm alm ereieie sfviers lisa ss) 49, 87, 88, 90, 101
and center of gravity........-----+eeeeeeeeeee 10, 11, 15, 46, 48, 64, 98-101, 103

BUCA 67 erece ececorersistainunker= 24, 30-40, 53-59, 63-75, 101, 114, 117, 134, 135, 137, 141, 142, 149, 150

7+" ws

no. 3 INDEX 317

PEREESUNC- SATIS OIG rats isicisre sah cies ayaa) nis-ehe.c, clove. 0 s.elee lace] efejelnie\ oleic laloieiel¢ wlsiateletelel ete ert a slp toteia cian male ia a lates tate
EAVGMUIV ETA Currant vectra; rclkl aye cicicieie tse aichd ole a wie wbivieisdveueleje OSe OL 6D, 00) LUT 179. 200 1 2OR 283
Provellers ..... 7, 8, 11, 18, 22, 40, 68, 69, 94, 95, 102, 103, 108, 109, 118, 119, 186, 139, 143, 145,
178-184, 258, 261, 262, 268, 2
CONMSLEUCCL OO Let vars lore ste tn se0 sts efsve, s.5, sic /s Ser suellsicts crs ei's)si cleto.ers, aicler ehansva ate? 63, 76, 98, 100, 178-
CATO TIN 87 O Peay. Soya e cies eis reais is rovarars) ey alea ye) & cherie) onc) enciwsusehe ereieue a) ols) <preiecs 1s\a smees ete 7, 8, 11, 22, 33
HOE TMOL Pc ercte cra clete’s cloves sie,0 se 61, 62, 66, 69, 77, 94, 102, 105, 107, 131, 148, 151, 189, 192
BULLI Sewanee farstele (a Vavors sictoreh es tereie edouat sho tieiiay oie ayera eleyavevatceerauerale ov sve oleae on eielesereare 63, 69, 76, 118, 181
POSUULOTAN OL perez cyapor ar Note eteraue <t<sdo\et’aps sey, valcve Gi aitherare/elsclovarns Die uiensios sarere/aaia Reams eee aaMee los
ERIS Ne “Ses aoe SOE Eh Cob ticle Gale occ CO eRcn war eie EIA Pir tee ea 3 39, 117, 175-177, 242
SSID RO Laneter reer NeV eye rela cace ae atay ss catia) aot ele: wists, o, choheyaie\ ns) ata ayeiol e1avoie oto Reeeen Feelin ie Le AEE eee 107, 109
speed of (see also revolutions per minute) ......... 61, 91, 94, 99, 107, 114, 134, 264, 272
tests of (see pendulum, lift, and thrust).
HIME Oo doe Stbla godine 0 GO DADE A GUO oS et ob 0 oe Coen Pere 47, 62, 94, 119, 148, 154, 161, 174
HO Varotrat-Pedoke Peer -xeetioyau onion cxatar<tclete e,Coils/ecacvechs) «sie lerey ofa Slekels esi avaltonavavpyevareus ier avetoveyerct svete 4, 8, 9, 21, 22
LTD Coma ona Ae ROD AR ee CHOC TOOT EEE Eee nene 36, 37, 57, 59, 65, 68, 71, 75, 114, 115, 141, 241
GOUT TATE Sin Goo Oth Og. OE CEE HTEIROIOC AOE SIS neN CSUR AIT ENE ec A OT ei ECS mir isin Ati: 241, 248
(SHIRE UIE * ois died b Hom Oe lo TOU OUOe Oka DOULA RORRIC OC aa aan ManeUneranurecanocGoUnlon 114, 244
OUD TE TACEIN Swreprerccetcte cre caterers: ofthe a: (alle tvpajla 8 saue1el siapsiions’ oyeraue s Diayacel or etp cide mb. etereterecale eieiein ae ein tiers 68, 114
RONGE Mar asteterstrc recieve leirertere cle is cic ev ie cialele Siisleivis)eueseleveis-e a -enejpiolelicle, so craveveleccle oretelelsinielelsparsteteiatctatets 57
Q
GemMAlte, Wey WEIS Elio oocosbeandeaccos GouopUOsauodbodDoonnenacasonc 64, 66, 79, 93, 147, 255, 269
QiraRler-sizeenIOd Cliserecyerars ele rekedeNeis pete) o isle («ies «)/s cle ieteie ies, «ies sie 158, 159, 170, 226-233, 243, 255, 257-261, 281
Quillerelersandaspruce rl DrCOM Pane” erercrelc tere =/c)1+1o)-folele\cleleiele eee) «)oleisieinislele\a sleleictelelelelinlele viele siete 200, 201

Radiator (see also engine, water-cooled)
Aan Cola hem Gone Wels ere eee ee per asia lolelolersts ove ofolalGint-cnreicichalo leis «leychenojeiai s\vis lel e\nlegrisisiel«isiwisletmleiaimiainl 27
Record of flights (see also data, sheets)... ee wee nee eens

RGEC eee Ch 1 Cin Campe mbelyam terete stelle leleiels(elaleiels:arl av) <\sefoln\slsiejevacs/s]/=

Tevoalh Aina they eb eo co Oo ae laos SU ODO OOED Coc tan cboOC per coupon cdEodeonme1toncooane 460
Relationrotsares tOmwele lt tyA GMD OWT eine icreleieie/s/a ereleleiaicisye mis sel afuyolaralelejelelsjaleve

Reservoir (see air-chamber and tank).
IRSsiGme Mile ccacssoansose danpenpeoe so bu ndoooo Ap obooaemEoUeonos boDcodesobaanaTone =

(ue ineshonvs Gyatal Faby PUR anc Sb.c0 moO nRaD ee AGobd onc So CoUudseOoddsccK0sboUaOD Rovere * Ye
Revolutions of engine and propellers per minute (sce wlso speed)....53, 08, 63, 65, 66, 102, 109, 115,
249, 252
Rib, spruce. and eagle’s quill; comparative strength Of .. 2... nee eee eens 200, 201
UD SI CONSETUCULOMMO fevers crieteier-lole cl erersusrs folate! clelele.s/=\o\a [else ole! 37, 80, 81, 86, 89, 188, 194-206, 263, 264
Ridgway, Robert, on American Buzzard. .......22-.. ses cee e cee ee eee eee ee ee ew ewww nee ncsceees 301
ING ARVEID Orn Valdes popoob Op CDOS OBOODOODD HOD SOUGOUOd non OnOr Oooo ooDS 82, 83, 91, 98, 100, 101, 103
RIG, TG Ol 5 - dacc ancemoup adn Sap bOOMeOooc UO CUCU A DDOnNObOSOOOdoD SoD b boca oo OnerbesEiaGos 61
CONC O LA Ore eer cke are Toler oe eeroterastones Gta syeteisyeraperaraval's ratoumiensversietsnct ke euarerseercteie s wpareiauela, 6 62
UB DELMAS HES OUT COMO LMO NEI ae rr cic ich ieterhelatetstetenaelota ofetele oie) <lelsiersislaielstelsfel clalelatefetarsieval-f= 5, 8-24, 44, 76
PEG ithe Or Ao gooaecwods Bo OO POR CCODAUD OM hd Ono SA ROaUDOOUCOOUECE BOD memos Hoadsoune 9, 22
SUG EEC Mame OST St peyote) <to etars clove seVeleiclione '« cataleraraleteye) si oleic is:cler~,clerele) okeletovet atatalene)alaiateletsiajetst=1=[a« =reValars 23
HG LSE DOW.E GED LOUUCE CMD Yyiyaeretersteleperelsteletetet tele otal oneteod-y eer oraleyelat-feletele | atele chet stelle atetotats satel 95 22,523
SMES, ci sdodoonadsanducocsouconoudnoteNNaondoddc dooseU Con AdanODaToeCnoronas DDD 0c 2, 185
APE. Seedenateadeate focte.cMoon GOODo conc ond RAO COO OPOOC OCS AGbOGOn GasaGcc 144, 241
UTEP DO Le Uta eOTUEI OG CLS Mee eer a taredmey tee cheer ciel ete iet ot slater e cei sh cticiets exseeliaral shalis/ciiarayeystieleteseiete wate: suer)eifa/a ovals. «ieee 5, 8-22
RUppersnullmandenubber-twisteds MLOGeIS sh jorclelelete te ele elaies\a) olele)s wlelble(e e oie + els elelajeielvisimiwlaieisin eis =ieiels ls 16-24
innolilse (GQaeaitymtnl Dy ooopeone cssulbancoD SU bO0o cob ooS 8, 9, 77, 80-91, 122, 136, 207-217, 255, 272, 275
ATOLL OTA ae AT Tyrer tian aeiodate cloreiclelerelsaveteleterontvonacieruiclekensivner shel ecausloitier= suche! avefepepiiavetels leslie] sie 8
Pénaud’s, 8, 12, 13, 50, 79, 87, 107, 122, 139-147, 151, 209, 211, 213, 214, 216, 253, 270-272, 275
rent Cale OLutiOsin OLciterbeterericisielelsteieiaierel svatereraiclsreresecs s/a‘s)s eis! bfole\nisielel=inl els 81, 82, 86, 97, 101, 106
Rudder-tail (see tail-rudder).
Ss
Sanding-tests of WiNZS.............eee creer eee rete terete tenet teeter eennes 84, 85, 89, 99, 190-204
“ Separator,” evolution of, for dry steam......---.... eee e eee eee eee eee eee 58, 59, 65, 68, 114, 142
Serpollet-type boilers ........ ccc cee eee e eee treet ee teen eee eee nee eee e eee 56, 57
Shafts, main, construction Of ............ccececcscececeece cece n ens cceeeeeenesetseenssseres 117

ORO EIG! on no cacirolo dbo (BD CUMOnD TOL ORO CO OCU UC DUN ROC CUUCUOGEOOmOrcC Or 39, 117, 175-177, 242

318 INDEX vou. 27

PAGE
Sharp, Archibald, on balancing of engines............-<ec+ecessecccecessecuscs aYalawiclalelelsleietocte ceC ao
Sheathing, .aluminum-.12% fcc sca joke elon cee eee eee Oe ee BosocAsosSOoAnS 69
MICE: * 5 srelerstage = cvoysie wlaeoee ce iia EE Ee rn eee Bobo Wh fe, 1b
SHOP LOSts a2! s- 5. 5.o/a.cle'cin clorcsaet alsin ce eae alee toe ae en - 40, 218, 251-254
Silkswing-covering *..0. 3c tees Poe ee ee ee 54, 68, 81, 86-88, 90, 148, 194, 195, 205
Sliding itail designed Sc. scan piiccetk wae sore pee ae cee bie eer eres 16, 84
Smillie, Rhomas iW: photographer. ern ve oe eee eee eee eee en 260, 267, 271, 273
Smithsonian Institution ....1, 6, 17, 18, 31, 42, 124-126, 171, 174, 176, 179, 257, 260, 271, 276, 280-281
SMOKe-StaCh oe! <2 5, acces tage, Sees ee Phage + A ae ee ee 60, 67, 74, 78 -
Soarins-birds, study, of (see\also|appendix)- ose a peer ee reer ee eee eee Sa. Wirt tote!
Soaring: speed: ai. se.02.43 e-nsgeis take eee oo ot ee OO EE ee er eee 32, 41, 69
Sparking devices (see electric batteries and circuits).
Speciiiegravityas ce ero eee & 55 falorajoteValtecs fax ceets are erage Teor ree re eee tore ree A iNetctoketers 120
Speed attained (see also velocity).................. 31, 32, 41, 55, 61, 91, 99, 107, 114, 134, 161, 264
Speed“counter® $5.4 ae tet aes ecto eee eee ee A eae ee 62, 120, 185, 243, 249, 252
SPOK Cs; WTO sre cctece sid:0:5 je Teves im Saveteto Slo cer Me cle ad Ree eS Tote oe 243
Spriiceguy-sticks and frames (Sis. ei hos cote, ee On ee 85-87, 90
ribs:compared swith quills 2.4). 5 seer ctor eer eae eee ee ea ee ee 200, 201
Si-. Louis Exposition tests. jcc. cathe s Ac ppl eee ee en 249
Stability lateral) and: Torei tu din alleys set -0n patie see epg ag 45-52, 77
Starter on launching-car : 2° .7.jcryeta o> Co seperate ore eee oak eke ee 94, 95
Starting-crankion launching-carv.-ey-nae ene eee eee ee ee 243, 244
Steamy dry, production: OF. ishz- rhesus oes eta telars teste Ee ae eee een na 58
Steans chest! oa aie weg 'saleiets sie Hy dcvayadeg eemteye ATs a ATEN A a ee Nn ie a a 117
SUCAMI AON SING HS. sacahs deve Seria ae ete a REE a Ne 24, 30-40, 64, 69, 116, 120
Steam-gauge SOOPER GROOCUDL ABA OAOOoDonnannon map oor SaSSAn he boaOOL OOS BAOG EC EGn UO bi iobe cod bee 114
construction of: framlesvand |v. pyrite ero te cicero ees 53-80
Steam-generating apparatus i. toard. ic «Asma vee brtun earee Aa ee re 114-116
Steam-motors and’ other models ajnan-5 doctor ae See 30-40, 184, 135
Steam-pressure ........... 24, 30-40, 53-59, 63-70, 101, 102, 114, 117, 134, 135, 137, 141, 142, 149, 150
Steely use sOfe ss icon cclan Gad. ce ie ee oe ee ee 69, 112, 116, 119, 121, 172, 174, 284, 277
tubes for “hulls. a. cee ee ae ee eee ee Pe OTS Osten en oes BEE GRE Yi, Gai abie ips)
Steering apparatus (see also equilibrium) andi icontrol)) -.-- assesses see olen. 214-216, 265, 266, 272
AULOM A 6 is kevacs.te. alsa eevee Oe ee 30) it, 2d, 206
Steerinecwbeel’ precisa ice chen ae eh nn een een oC SANS eee 214, 216, 265, 266, 272
Storage batteries (see batteries, electrical).
Stringfellow: Cneine’ eia.2 33 o> ort.cdic pence na Oe ee 30, 31
Supenposed!winesic faccercice esto heen eee nn ae 13, 14, 17, 138, 158, 193, 231
Supporting esarlaces seis, sient see Sea eye eee ee re em 11, 44, 77, 81, 99, 188-206
Supports” for{propellers’*-\. 7 as-.a nv eciae dose ohana an nn 112
Wings (and stalls: . clans.) sealant etoeine sect ee oo en a 36, 69
Surfaces (see also planes and wings).
COVEDINE fOr drtisctretoete teers oe ahs eee as ME ee es 77, 81, 86, 87, 90, 148, 194, 195
QUIVEU = ersvatepe eens St Sane AS evejeist aie ete IN Ei Re a RED ec aE eT on 44, 46
plane. observations on WEIOCIUY Ofte craie, “a y-tevc in alniehs toschetate cic oe vote oor ton eae ae 1
TALIM oe Fic carat siete ehevenec tyra tessa crty e yee cera et a 6, 46
BUDDORUINS: o/< srctevstoyahetaxstese nia ote Cheer erase ane ee eee sen 11, 44, 77, 93, 99, 188-206
SUSE ATM corer oo ato oem ee Gaal EC ee ae 1, 5, 41-44, 80-91, 99
and guiding 2. yycasons ccneed ace eee Se EC ne ae 5, 80-91
Surgeons’ tape, used for MeN GINS TIPS ye eather, aks steppers la aot eee 264
Sustaining ‘surface’. 5.5 Shite cae ee oe aE oe a eee 1, 5, 41-44, 80-91, 99
de Lucy" onl fs Scere sare bless eee tote creme ee a ee ae 19
SYMBOMS'r 52). oo 3 sate ow essyel ns We erate bola CR eotaee OP ete aoc ats ea aa 14, 15
Synchronizing mechariiam* 0? 078.251. s0 ns eee eee ae ee 108, 121, 136, 137
Tr
Table; ture 235 5 2554.0 55 siessiareltie cress cio ome eee kN Eo 156, 165, 166
Whirling: 3 (crac unre Ieee eee ee 1, 5, 6, 7, 11, 18, 31, 42, 165, 166, 178, 189-194
Tachometer 7.554.325; nema sesec ol te ae 62, 120, 185, 248, 249, 252
Ped ooo ciaGin. ne alivs Spore eh aaicit Sho Se ee eee 8, 9, 70, 77, 80, 91, 99, 207-217
adjustment Of (50/2936 5. 24.0% aslefelsjty SIH eek tes Aree ee Dee 16, 84
Conmections 'Of" oh 7a telalere see's olstars Tote ae eer ros eee en nn 84, 213-216
COVOLEDE os) asuis'a's 5 slivierea.« aaials alae ote otole ho) ape ene ee 86, 103
Pénaud >). 232422 a eee 12, 13, 50; 79, 107, 122. 139-147, 151-153, 209, 211, 213, 214, 215
BULGE i235 js’ 5 siciae al secoPe sede lela covooiee ee ae tea 16, 84

use as guiding and sustaining surface..............ecceccecceccee ots ia\(eleselulsnta\sa/ayvaveleveyelatate siete mee

no. 3 INDEX 319

iS PAGE

GREG . Osea oes 65505 OS BN OOD oo DOSS OAT Jao Seo OOOO Ot OGCr TOULOOFCC 77, 86, 87, 119, 152, 153

: IbGINEIES, | BES 6 bo Anos SEO DODCOT ETUC OODUDD ORC one CeO OUdC On Jo C00 c JEnOUCre UNO Ur ON OUC. 77, 86

“alma bbe Be oeee Se nT Cars TRS fecha tetra eva losctonevanstcsaieisvaterdiciecetetels chatera, a) efarehelevel six iesa 64, 68, 69, 112, 114

MMA 554e 054 6a 00Go0.0 66 OOD OD SOC HOG CUCU COG OO ULTOU UN OOOO TG Om COT OOD 36, 65-68, 112, 113

TING Cagod beaded atop oO dUn os cob pnocmod Ooo rondo fo” Uno POOR Onur CU rOUDO UT OOG ONCOL OS SO. atc & 252

TEANNOKG) CENT Goadooqnoosgocodgen EH sUndNe sou One 20 ue -nodU sp pC OOUOO UCSC DOC DCUUGt 260, 261, 273
Tests (see also engine tests, trials, and flights).

Mie. ce bo boa bone On SOAGO CONS Do EME OBdUD CUDCCODUO RES Ucn COOUUUC OCHO OO Gn OU CO. 70-75, 135

OLS URITC UT OTUATLC Marpac rare tale crcictetarcictelcicisieteretetetote stovel-t=] el ssel~Seteiny='ecaneie 9 jagalseiohd nlolexal&. o7a/=)e)=halaiale 234-250

(ayllinGar” sgosnonroromaboneeqs oserouasaouy Oe AO CONS OOO TD UG OOR DOOR DUG OuG OIC CONES 55

PUPA ilaycinie s eie elerelete) elainiels's)sls)s a /ale le sieeve 37, 55, 61, 69, 102, 133, 135, 148, 234-250, 251-254, 281

experimental engine, 1902-1904 2.2... eee caer eres onesie este ne eens s sees ser ensaes 250

GERI.) Coots SROON COR RR BR CAR BRD? Oooo seg bo t.n St 40 0 ONEE DONE DOOD OO Demmi OOOt Grn ssi ycr 79

DOMES 4 dancoue oabsdubocosens ond GEe™T ecu Ug e OOOO UD DAOC KEnE UU Pino aiecO ROG 61, 62, 69, 102

ERGO. “bod soso dseaodosine Jocescoduopp ono godur eC CCOC ON OOO ECOMCO OAC Om Ig Oi 165-167

RainGbosts, Ol wallace ao boooonoougT oot SoeoccnboUdodU OND OO UCue SDM OLUCOOCd 3 $4, 85, 89, 90, 190-204

Gyo, Gin lendeto) 1selonmtlenn oa phono eSedsu0 Dot COU CU EOE OGo yO ED EmGODRUCOO UE IDG 40, 218, 251-254

Si. IWAMite equa inOnln woes oben Daas ees oNeoees adcbD.co DOO UE ern on DOCCUnGOmEG rE OZ OIA Olk 249

Whirling-table a... «ccc ieee wire te eisieieeisine eles dba Gs 7s Ldn doy oi, 42; ediGb-166; 178, 189-194

Wales) peobooocococnogpesubcocuraoo GOO U0UI Ob CUKdo Db CODD ODOR Dt II: 84, 85, 89, 99, 190-204

Testing ground (see also Quantico) ........+eeee eerste reste 64, 66, 92, 93, 255, 256, 277, 280

TUNA CMO Ober bach obdesodd dace Jueeonobads Ot CO bc GN CUR COOOL On RGrr Die GOK VCO ae af 62

WHO WAL, Bonde somo a Joo Seno OOo CUS On DUG DG OU DOH OUGLG 47, 62, 94, 119, 148, 154, 161, 174

HUMAN MEA TTIb TE AGA SKOSS ousid bane obo AU Oo UTOOpROODe OCS CC COCUCD LT acmls coCoU Gk armel DOC 229, 230

TMiMASIO Tee elon oe sans Deuba be bOU oe DOL BQUB OCS ROS TO ODOR SC HCCC ON ia Tea tee Sa ae laa 128, 129

GMN® OF sili ahocagooopod Da nbOOD CoeDSUPOO QI DDOH ODED OCAGOC 103, 107, 108, 109, 137, 145, 148, 258

TORTI! Soe sou do nOadeashHoOn ODO pe TOON sOs OGUNC ObTE SCOT UT OUt GONE OnS DOM Sea aa rau ie ae 222, 242

GRan? DORAIEINE saans Comp ade hoaUb Rope o PEO CUOROD CUUOCE OLA RBC Mbt JCOCC CESS aI: ok 7, 9; 21, 22, 40

Transmission (see also shaft and gears) ......-+.++ seer rere tere e teres eres etc es 117, 175-177, 242

THPATIRV CESCMEDATNUG ee ciealcerckersrcicie ele ete ravens iancia aye elke, ofehniiset sel muavernmvic en cieestin a CCl Riacrsicncyes 77, 165, 174-178

THB, MES, mao cn odaeW ecb bud sbobueO oI popE phe D00N OTOP) SOLU OG COS SG EI EE ia ia sal dea 97

(HIREHID) ae yacblosatod deoad sdoenbpoacdtoves6bG 40900 0G 00 Ub o ump COs OIG OHO soo saa 17

(HIRE). Gaceoocbhgaduosonodbausode te Sono noUchGpGoDd. A. Doc Op Oe BODE OS Ra ann oe Nas 58, 92

(EATON) Wy SL wai co odanne pateoD old ere o0Iso arto ie RUSTED ITO SS Uae i Re ah 65, 93-96

(HEV) ened Pdo oem ouoaraccnoaucecet cnetcm amor tbgo Sgro c oC Oni Rina teas a i 65, 96-100

(HIER acto Senos oo wearesa San Od ocin poo Sodas aaa ODObOUO SaaS OTC ies ele sae 101-106

GEDA bas con como oncen sdbo Dood abesd > CoO OU Sc oUEt mc UDO CD Yue UDO boc amma: 2, 79, 106-109

(GIG Hetels sake nonce Omebane aon idoeMsoOnDO UCP OR On CORR paar ST ogo OS IPS sa ae aa 123-125

(GIEQEN: wochce Ba odeee 8p Go Coop onan 2O0 SpOdURG Pu AEOUOGGEES SS OU COTS BOD AA Gia a 61

(GUO) eeesdeorccercosugusdeupcstiee ce GOnU CO DCS CaOUG OED S Ie GOO. ROTO IEE es 79, 135-155

(IMIR) SB ededduooosanedsoub odumuneno nop obeaosoo OH COME Gn scutes oH 9 FOr tok 126, 181, 255-282

Tubes in hull construction........-----+++seee err e reece 69, 112, 116, 119, 120, 172, 174, 234, 277

Gini so adasetooe Coe Ades po SoU oupa ance yO OU E aro OO DODmE SUR ODEO AG0 ay aA CaS i Ek 156, 165, 166

Gremio (ae Wie UNDUE) 5.560020 9d oot Oo GOO ODDO TE URUCO ROSIE CUOUO LDL IG Scie Sos 170, 171, 172

V

TIP GLTIER: Sc budotobstes ob ost oUSaenc ous uCeEDOOpCU SOE En Co OCMC UR COON CRUG an sian oe 114, 213

SU ea OR ea TTT e ee Torede here Totes vel store ele fosniataraicyaseietaleasioiete/siezesacteleivieiaieich) 4)5tS! ates * 3 114, 117, 213

ESTHET) nis oe bio aaa Unoodd DED DOU CCSGC ODO Cc COOC DO AOO NOCD Ono maUOU RUD pes 2s ay 237

ANECHATIT CALL: OPSLALEM! y\efckepslessta cre stole) fo! olathe’ sleless/eiels(ornioloxece| min ohcie/=i0/s| Stes) eases!) AA aise 114, 213

GIO oO koag BO sabes A Coren OOOO MS USD 50-00 UGH COR OOO SSUES Ogi Cs aa 112, 114, 115, 213

TI) 4 bb panodidoe CGOSOO ON CUdEBOe Sc OOD OUICA DONIT OU Opa Gr caC Drs caer 56, 57, 113, 212

WSCA JugdosnsscccuasaoohnbaDdooueesoRDH ONC OOU NOOR DCO U COGS GC ies ig aa 37, 67, 148, 149

Whranlmuaa lnbiyn 65 oconsducaépne cob ond SOC CRDOUGS CADE OOOO Ot ao AAG i tama: oceania’ 192

ANE EMCI jn EMUAOWE, nous 6c0ce00000000UG NOs Dot CURR RE OO Ot CUCU seo gaa 198

URURONSC es copeoboone oobe 5000006 UdSOUO ER Goby TUR eay atic i Ole ii Sala Baas ary 86

water-proof Re eet ciotars ee cinseterafois cise serie panto Seaiaisp eats Satie Saat 263, 264

Val acl byaiicnrsc mite ait iataletetatace toe 18, 31, 32, 55, 91, 99, 107, 109, 114, 134, 150, 161, 166, 185, 264, 265

SAVIN ces bee tO BE Wott Gmiad\C CGR OIRO Or SO IO CLIO IEEE ea es ae a 100, 110, 150, 163

mequired! to sustalmeplanereemtlltliclolsjr ey ene se ened Ci 1, 43, 110, 166

Werticalorud derietdete scsertet tele eletarstoevatetleyeteivicialraeiern wiciyels fore ence a IT | 81, 82, 86, 97, 101, 106

Fain hoy TSE WO) NaS One ona o 6 SO SU CTE ePIC OOO SCS TS OI i allie 257

W
Wan Department, allotments 7p -r meee clases isonet IG 124-126, 132, 278, 279
Board of Ordnance and Fortification .....----+-+++srrsrrrrr rte Weed

Report Of 2.0... 0ec+s- se nter sence: 276-280

4 A
- a
7 7) : i
390 INDEX vou. 27°
PAGE
Washington: Evening Star; report, Ofte ccs cicero oles eiele tote tales ele fo ele ale to n ta oteeloye mialeiaotelelstatelaterie 274 ¢
Watches, stop, for timing: flight % <.0c ie eyecare ores aie io lateim ae oye toledo eee Sa efeleictetelste(eue UO aa
Water, cooling, tor engine. seracc cnn cilheielee cee ele eine ee eee te eee 235, 236, 241, 247, 248, 252
Water-engzitie, Hote ccc. 2 oncioce ccercceiose ier (ere falesoto ele eve te ate NSE ASS eee 24, 25°
Wrater-jackety cisco. cr lata cic qi Sree re tele ve pale Ole Fe fecal Tate eee tie ete ete eee eae eae eee 220, 234, 236
Water-proot -varmisne <ccic.c-oecesarere otarssetoreieveteyoicie sien elect ee berate Oe ee teeta ete 263, 264
Water-tamlk: ccc vaceiete coe cco sles aute. oleate ye eyeseca en eietet oes eieeny shee eione alee genet aie tet a aiken nee aeetat seeee 202
VENA Ch: Ain eal) ee Pea A rao nOG DOOdU ond somos dddconehos shoaucogcsaac Ashoaoe (et!
Weight (see also data sheets).
flying, of aerodrome....15, 38, 62, 63, 76, 77, 81, 89, 90, 91, 101, 109, 116, 148, 206, 247, 250,
256, 277
OF ACTOMFOMNG oso... erarcrsvenvranny= she elo eriale eie 31, 38, 40, 53, 62, 63, 116, 126, 130, 206, 256
COVELINE LOT. WINES a svnverccorcse,aiela-cvey atevevsuevetebeyescuste tome ores lobe lenetetere Braet ieLs eRe TAA aie eS ee eo 194
parts: of -aerodrome sian. cana aceaciilens-tee eee Ree ie 31, 63, 116, 190, 250
ONSING FF -12e aa spometee awe «steer ene Gea er eee 116, 117, 126, 130, 156, 209, 247, 250, 277
Per HHOLSE-POW. OT ys) < mjc o/erwrcyeisreteet er crebeteyatietelehed<feyouaycheyenenee pence tote fake Teta ets telearey aaa ea 31, 126
relation. to. area ;and POWER oo oc.00 eres aeteeele ee etae enero 43, 44, 64, 81, 89, 90, 96
total, with <Aviator oc ccie ok 5 js: ols. a ince: oreypsuers mlevossiebepaussessyeheechosdys ever eteReeye ate tial enals iste leretaler ae beyetetvstaeets 256
Wellner, Georg. .o.o.6i5 0/60 aie ire scnte oie 0 a/ele «i aveiera ays oetvess us <]oye Saseok pp Te ereeoteke teie oisie el eereee ve 44, 47
Wie!) AY cre Ss iesisee ie ey once pan ivaporayer sr eneirauesei dud sy ves ayed oy cucyscsususns Ouse k cee deu eset tes ezeyeetteney sete Ee vatete 242, 243, 247, 252
SECOKING io ccc peecie Siceys sie sa chose isd cuevaset ore seaparshop ster etepe eben gale onstele encod aeistererars 214-216, 265, 266, 272
Wihirling-table: - 222.55. s2:-lor., wets sto apt ocr false sated stale eae 1, 5, 6, 7, 11, 13, 31, 42, 165-166, 178, 189-194
Widewater, Va., experimental grounds) (1903)... mm cies re rere doieiotsl cpecicis erie ee eat aie 255, 256, 277, 280
Wind, artificial 2. o :5s. 65) sjs: s/s) Slayer sesarewleyeserapous aies Bros ouavel or lara taperer=) ete clees eaelctee kee eee een tere 42, 61
difficulties: of launching anlae<- .-\:csee ne sesso eae 94, 99, 265, 271, 272, 276, 282
experiments) ims stehe cigs alee aie tel oe athe eee lee iets otie ener 42, 61, 99, 257, 271
Mnternal work: of the. ....<.: is cacsndeoeodote Geen cee te nee een 6, 42
ODOM Fay5 5 sisvavs sraravey crate tore male ete vrale eee poner ne oe] ate ENTER SIT pe ucnS PACE Tenet eevee 42, 99, 257, 271, 272
Waind-shield’ for: DULMeNS’. of) .c)-/yozneissecteren cee eR ere ROTO rat ener 60, 67, 95, 115
Waind-vVane rudder, «oa «)ajejeecieve ayn terc ores syeun coop sicletv ny aveNSesTe/ettval eel reliever tetetelerstckeheie teva arene ale fatten 136
Win g-elami ps) «6:35 is! scare yaaa v0, 3 ele alin fal etoye rab tiectie ela Shake ol Lp SI TSE er ore oe ose ois iere aetna Teeter 82, 89, 145, 183
Wings, adjustment. of, for, centersoficravity sas. <n deleeo on cee cree eee eee oe niece earns 16
BM PVG: OL v5'srssierstorals.a.arshavetapara ova olor tole oie one eae 45, 61, 82, 83, 89, 91, 97, 98, 100, 101, 103
ALTPAN SSM ENE OL: s,o:o(.. «: orer0i erste. aieta sal soe ara sheccalcderereiel cere gererere che heneeetene eran PaCS 45-47, 77, 86, 89, 194, 255
Base INS LOR: ssp scece ce: avavsvacsitn auss saa rafares ara alert Aetene eye acey eters ones tate eet otote ae ete ate 84, 86, 100, 195, 203
bird; iconstruction. Of <.2%,.5 6a ane rane ee ie oe ee ee ee EEC EER oe 7, 188, 200, 201
Le) (ch) Sere Mo ican os oat omooc ocala bomb arson ope onaAnAonCooos eto” 263, 264
CONSiNuCtion Olge-ns eee erie renee 7, 70, 80, 81, 87, 90, 91, 99, 105, 119, 121, 138, 188-206
covering: .of,: Cloth, . 0 a)sies we cisvate seca srerterlsveloeleretetc sar yeloeierstberiatsereieeeare orators 195, 199, 204, 205
Boldbeater’s SHIM scsi. icc cies tepevey era ercvcjese ater Selers wyeraleravale olelavors sho, svetey stalerePal tT T oR ERe 77
PAOD, oieie'e, ov ele co; jhe ols, ofa b icles sueterebe Nejene es ITS closer ctosciolers CRIS icici teeth tol en en erat aens 86
SUT ois oie vare Sod i bie Shere aurea erere realtone one 54, 63, 81, 86-88, 90, 148, 194, 195, 205
WELZ OF in in aie ezeiae o, svavsunts oyanciere revetaters sare seiareieye lotelenetehoteae eles eteke fore aietaiste Paneer 194
CUIVAtUTE Of oie) 5 0% Gi elew sie ieis: srciase, aldose enetetarsttedetictetaleetteiecieniaters 18, 44, 46, 47, 86, 87, 90, 99, 112
Gistortion sOf A. css wis secre. cave ease ee Eee eee eee eee 82, 83, 84, 91, 98, 105
Gowblettionr .1... 5 sivissjocitys omeitoommnyelst Perse Meiaerea er ereretke rere ei retreats 13; 24) 17) 238; 198R 231
@fF CLEMO y Of) Ho sicis ciate scpere tis! dyn; slaraieless eheste epemetsTA Risto tetera repre hee 46, 87, 89, 91, 144, 192, 193
flexure of (see distortion of). ;
pocketing. of 0.2. SSCs ork son acd etorare rel ceateve crete ototetet etna ser biere eel Tee et 84, 86, 100, 195, 203
quills and. spruce ‘ribs compared): 6.4. 5.55 ncishca cit oie © sie ere were Sate eral ts vie ayeheievenayete eterete 200, 201
1 | 2) arr See noe niseron nbcick so ubmrcooeoD ode 37, 80, 81, 86, 89, 188, 194-206
single: tier’: tats stators ns were ere ees 17, 142, 146, 147-151, 153, 192, 193, 231
BUDETPOSOM ose). es. ers siete creawe «eisiene rececuaie te arene eis ae ne oes ie rere 13, 14, 17, 138, 158, 193, 231
BUPLACE: OF win. ils Lee aic ca Gis sin ererw outpevacoravere ialentie, Maser eae Seat eiele MLE eIaTOVS: Stele ers Sete eer et oe 9, 69, 81, 99
tandem efficiency Of 255 00 65.005 eS bitis Dee tccbre ew rennin ra ere ereneee SP aie ETI eee ME ST nea ete 46, 87
EWO BOTS OE one seccss5:5. 8 are.c rs See aad orhrecd oe are le reuave ai are amas aust Bene e le tareticteteetstene tetete 13, 77, 106, 138, 231
V(t 4a) en Mee rnMne ttre Aso korcsry tr odcocdc coo ono oadmodonospogcoe 190-196
Wire gnyitte.” 5 Jeng arene Care meee 81, 84-91, 99, 164-173, 189, 191, 195, 196, 199, 264, 266
TESIBEAMCE 06.5 ejeice aoa w'ele nid Sore aja woo: erays oes cro Pe OHNO MCI ey uae Rete aie teense Rete ees satel tale areteeetctonete wee. 165-167
) )):<:) e e SoenonnrarManionsa Gon nos on doce ag oucte cea soourdoorooucsc0™ 243
Wooden Buy sticks) 5030 \555.0.N0 55d 2 aS cers ecb Rie iets ions Oe So Ee ne Eee ere eee 63, 81, 85
bY | SAMA aa tc chance doe oc cooue 37, 80, 81, 86, 89, 188, 194-206, 268, 264
Wrecking’ of large machine..:......0%44.<4..55226%2+ ee TOP RPE ee ee eee ee Rete 126, 184, 265-281
Z
Zine, energy developed ‘from: «5202s .s/on2e eens sss Me ce eee ae ee se Re Te nie eee Tile gee:

Zoological Park camerasc:... $< ses. csnd a macive celenen eae COROT a eee 260, 261, 273

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